Last week I installed Lubuntu 12.04 and have been delighted with it.
Now I would like to install an ftp server and have been convinced
by reviews on the web that vsftpd is a suitable program.

Unfortunately it is not listed in the Lubuntu Software Store.

I am not very confident using the command line so I have some questions:

If I install vsftpd via the command line, does it do the same things as an install via the software centre?

Is there another way (GUI) to install software that is not in the software centre?

Lastly and perhaps naively, why is vsftpd not in the Ubuntu Software centre?

installing from software center and command line is the same thing.

If you find the .deb file from the website of whoever makes the software or from sourceforge, you can install it via the GUI or double clicking it.

you can just jump into the terminal and type

1 members found this post helpful.

Actually, for a .deb package you need to type

I use it myself for my home-server, easy to configure and reliable.

Yes.
Yes, you can install the Synaptic package manager.
What shows up in the Software Center is decided by the Ubuntu developers, so we can only guess. I would think that they just don't expect people to install server software with the Software Center, since most servers don't run a GUI.

1 members found this post helpful.

I think vsftpd is in the software centre but you'll have to look for vsftp not vsftpd. I'd be surprised if it's not in there since it's in the Debian repositories, which is what Ubuntu is based upon.