Usually the ATCO's are also people passionate about aircrafts but is not always the case and at the beginning there are a lot of aircraft to study in order to provide the correct separation for example during departures.
In all my life i've been always a airplane fan and i always look at the aircrafts when I can see one, for me isn't difficult to study them but I found some easy tools that will help other people like me to study them.
First of all I wanna to talk about all the books that you can find in the market, like aircraft dictionary ect, are very common in the libraries, another thing that you can do is visit the very famous website airliners.net that has a section called aircraft data that you can find here, in the same website you can spend thousand of time looking for all the pictures in the database, probably the most complete in the world!
I also found very interesting the gallery done by the user caribb in Flickr.com, in this gallery you can find a lot of specific pictures of the most important airline aircraft, here the link.
In the end I will talk about the database prepared by Eurocontrol and free to use for everyone, in this database you can find basically all the informations about the aircraft that are divided into different categories, together with many pictures you can also find a table that will show you the different performances. I found this tool very easy and powerful considering that is free!
Eurocontrol Aircraft Performance Database