Many times softwares are hosted on ftp servers, especially open source and not so popular ones. FTP servers are also good method to transfer files and folder between machines. This means that you will need to occasionally connect to FTP file servers either to download or upload files.
If you happen to work with FTP servers a lot, then it pays to install a FTP client that provides an easy to use interface. There are a lot of good FTP clients out there that serves the purpose. Filezilla, gFtp, ncFtp are some of the popular free and open source FTP clients. If you need to do this only occasionally, then it might not be worthwhile to install a dedicated client.
Many of the file managers and web browsers that come installed in Linux usually have the FTP support built into them. This means that you can use these as the FTP or File server browser instead of a dedicated FTP Client.
If you are using KDE as your desktop environment, then you should already be familiar with the KDE file manager Dolphin and the browser Konqueror. Both Dolphin and Konqueror has built-in support for the FTP protocol. You can access ftp servers by entering the URL to the server and specifying the protocol explicitly.
You enter the URL in the following format into the address or location bar: ftp://<servername>/<foldername>/
Nautilus is the file manager for Gnome desktop and it also has support to connect to remote machines including FTP servers. You enter the URL to the server by explicitly specifying the protocol which ftp. So, you will use the following format for the url: ftp://<servername>/<foldername>
Google Chrome/Mozilla Firefox
Several modern web browsers also support the FTP protocol. You can use either Google Chrome or Mozilla Firefox to connect to the FTP servers just the way you can use the Linux file managers. Just enter the full URL including the protocol into the location bar.
Just as before this is the generic format you will use: ftp://<servername>/<foldername>
Once the page renders in the browsers, you should be able to click into different folders and download files from the server.
Command Line Interface
You can also use the command line interface to connect to FTP servers. Technically these are known as command line ftp tools, so it is not true that you connecting to the ftp server without a client. However, most Linux distros come with a default ftp tool installed which means you could use it to quickly connect to local or remote FTP servers.
Again you will use the URL or server name as command line argument to the command ftp. So, a typical command will look something like this
$ ftp ftp://<servername>
Once you have successfully connected to the server, you can browse around the folders using ftp commands and download or upload files to the server.