The 'order' of licences, from lowest to highest goes like this:
(NPPL) - a special UK only licence, restricted privilages.
PPL - Allows you to fly for pleasure. You can't charge people for your services. You can't even do some things for free!
CPL - Now you can earn money as a pilot. Woo-hoo.
ATPL* - Now you can act as a Captain on airliners.
There are ratings that you can add to a licence in order to allow you to do more things than the ordinary 'Day, VFR' limits:
Night Rating - You can fly when the birds stop.
(IMC Rating) - UK Only - You can fly above clouds and in poor visibility. A poor-mans version of a full IR
Instrument Rating (IR) - You can fly in all sorts of 5hite weather and in controlled airspace.
Flying Instructor (FI) - You can scare youself by teaching other people how to fly.
* An ATPL is, in essence, only available once you have got a CPL, an IR and have completed a 'Multi Crew Cooperation Course'. There is a special study route that allows you to combine all the theory for CPL and IR and take the exams just once. This is comonly known as an ATPL Course, though you don't need to do an ATPL course to get an ATPL - you could do the CPL and IR separately.
Thats it, in a nutshell.
