FTP - Setup basics
Blogger needs three things from you to FTP (well, five if you count username & password, seven if you count archives, but let's not, just yet...).
FTP Server
First is the FTP Server. That tells Blogger what other computer to connect to, nothing more. What that server will be depends on your host. For some hosts it is the usual name with www replaced by ftp: the FTP server for www.geocities.com is ftp.geocities.com. Sometimes it is exactly the same as the usual address. And sometimes, if you have a "virtual domain" hosted through a hosting company's address, it will be something completely different: the FTP server for www.ringnalda.com could be ftp.bigolhosting.com. Your host should have told you what FTP server to use when you signed up. If not, look on their home page for a FAQ, or technical support. As a last resort, call or email them, and ask. Enter the FTP Server as just the name, don't start it with ftp:// and don't include a username and password (phil@ftp.ringnalda.com is just a way of passing the username in the URL).
FTP Path
Once you have entered your FTP Server, you need an FTP Path. This tells Blogger where to put your blog file, relative to the directory that your FTP server puts you in when you first connect. Some hosts will automatically put you in the correct directory, and some will not. Also, if you don't want your blog in the main directory for your account, you'll have to tell Blogger that. The easiest way to determine what your path should be is to log in to your FTP server with an FTP client, like CuteFTP or WS_FTP. Set up a new connection, and only tell the program the host name and your username and password (after all, that's all Blogger will know until you figure out the path). Connect to the FTP server, and take a look at where you end up. That part of the path is what you don't need to tell Blogger. Now, what do you need to tell Blogger? If you are in an empty directory, then Blogger probably doesn't need any FTP Path at all. If you are in a directory that already has your web page(s) in it, then Blogger certainly doesn't need an FTP Path. However, if you see a subdirectory with a name like www or web or public_html, then that will be the start of your FTP Path, if not all of it. Some examples: if your web site is at www.ringnalda.com and you want your blog at www.ringnalda.com/blogger.html, and when you log in to your FTP host you see a directory named www, then your FTP Path is www/ - nothing more, nothing less. If your site is at www.geocities.com/ringnalda/ and you want your blog to be at www.geocities.com/ringnalda/writings/blog/blogger.html, and when you log in you see that you are already in the ringnalda/ directory, then your FTP Path is writings/blog/ and you need to be sure that both those directories exist before you have Blogger try to send files there. The FTP Path is just what you would tell someone to do after they connected to your host, written so that Blogger can understand: "go to the www directory, then to the blog directory" is www/blog/ in Blogger terms.
Blog Filename
The final thing that Blogger needs is the Blog Filename. Blogger thinks it should be blogger.html, which is fine if you are going to put your blog in a directory with some other files, including your main web page that is named index.html (or one of the other default page names). If your blog will be your main web page, or will be in a directory by itself, change blogger.html to index.html so that you can tell people to find your blog at www.ringnalda.com/blog/ rather than www.ringnalda.com/blog/blogger.html. Whatever filename you use, be sure it's the same in Blog Filename and at the end of Blog URL, which is the address Blogger uses when you click "view web page" to see whether your blog made it to its new home.
Username and Password
You have the choice of putting your username and password in your settings, so that you'll never be bothered about them again, or, you can type them in every time you publish (or maybe it's only once a session (it was annoying, so I started always putting mine in the settings)). Some people are worried about having their username and password stored on Blogger's server. If it bothers you, go ahead and type it in each time. Just don't think about how sending it from your computer, to Blogger's server, and then on to your host, lets twice as many people have the chance to intercept it. If horrible things would happen if your username and password were compromised, you should not be using Blogger. Send your blog to a free host, or a paid host dedicated to just your blog, and link to it from your site full of secrets.
FTP Archive Path and Filename
Of course, all that is only enough until you turn on archiving. Then you need an FTP Archive Path and an FTP Archive Filename. If you don't mind having your archives in the same directory as your main page, then the FTP Archive Path is exactly the same as your FTP Path: nothing if you don't need one, www/ or whatever it may be if you do. If you want your archives in a different directory, then your FTP Archive Path is just your FTP Path plus that directory: www/archives/ would be a reasonable choice. Be sure that the directory exists before you try to publish your archives. Blogger won't create it for you. The FTP Archive Filename can be anything you like (as long as it's a legal filename for your host - lots of free hosts are picky about the filenames they accept). I like archive.html - the archives/archive.html is just confusing enough to keep you on your toes.
When things don't work
If you figured out all the things to tell Blogger about your host, and everything was right, when you Post & Publish, you'll be told "Your publish request was sent at" the date and time, with a link for "more info". Click the "more info" and you hope to see "Transfer successful. View page to verify (give it a few seconds). [FTP Log]" - click "View page" to open your blog in a new window. If your post showed up, congratulations! You're done. If not, go back and click the "FTP Log" link, to see if that will tell you what went wrong. Since Blogger thinks the transfer was successful, you either put the file in the wrong place, or your Blog URL is not the same as the place you told Blogger to put your blog.
If you didn't get "Transfer successful" then you should get either an error message from Blogger (Error 210, etc.) or a "Transfer Error". If it is anything but "Transfer Error", write down the exact error message. Really. Write down the whole thing. Sometimes the error message doesn't tell you anything, but when you post in the Blogger Discuss forum that you got "a 5 something error I think" you'll have a long wait for a response! If you got a "Transfer Error", click the "view FTP log" link, and look for the part where your FTP host became surly. The most likely error is "553: no such file or directory" which either means that you didn't create the directory you told Blogger to put the file in, or you are trying to put the file in a directory where you aren't allowed to put it. If you can't make sense of the FTP log, copy the entire thing, and paste it into a message in the Blogger Discuss Getting Started forum, along with your Blog URL, FTP Server, FTP Path, and Blog Filename. If you are concerned about security, delete the "USER username" line in the FTP log before you post your message.