I can't believe people have to ask a question like this, this is what Google is for.
I'm sure you've heard of different airlines, search for their sites and then look for what you want. Search for flight booking in Google and you'll get a load of links in seconds
A tad harsh Cakeboy - the key concept the questionner wants assurance about is that they have never booked a flight before - always used a travel agent.
Evedawn, also try http://www.ba.com because if you book aflight far enough in advance it can be very affordable, and you don't have to survive a rugby scrum to get to your seat. Oh, and you get a bacon butty or equivalent.