Using Ubuntu Software Center

Search for openssh-server in software center. Server related programs may not be shown in default search results in the Software Center. You may have to make sure that technical results are visible in the search. There should be a link at the bottom of the Software Center window with the words "Show nnn technical items," where nnn is a number.

Using the Command line

Open a terminal by pressing Ctrl+Alt+T and enter:

sudo apt-get install openssh-server

Unlike the GUI, the password prompt won't show anything like **** when you type the password. This is normal.

The two methods of installing software in Ubuntu do exactly the same thing. A lot of people write command line methods in answers because they are easy to copy and paste in the terminal and easy to describe. The server installation does not have the desktop, so only command line works for both type of installation.

For FTP server:

I recommend using sftp. This is more secure than ftp and is part of ssh. So you won't need another server. Another advantage of sftp is, if you setup private/public key based login for ssh, the same system will work for sftp.

Otherwise there are many ftp servers you can choose from. I think making sure the "technical results" are visible will show them if you type ftp.

see Basic Ubuntu FTP Server and How do I install a FTP Server? for various other ftp servers.

Hope this helps