Can you explain the difference between a socialist, a communist and a democratic socialist (LI5)?

People seem to throw the first two around a lot, often times using them to describe the same things, which I find confusing. Despite this, other people have told me there is a difference between the two, so if so please explain. The third seems to be the name of a group of political parties in some democracies in Europe, however I gather they have different viewpoints than socialists or communists.

edit: I've been informed it is a Social Democrat, not a democratic socialist, that I was asking about, sorry about the mix up, as I said it's late.

Also, please excuse my poor grammar and crappy spelling, I haven't slept.