My Mac is getting hot very fast, and the fan is loud.

Hello,

I got my MacBook Air, around one year ago and a three months ago. I use it for school, and to surf on regular websites. Sometimes I watch movies on it as well. It has worked fine the first year, but now as soon as I have used it for about 15 min the fan starts and is very loud (sounds like a big old PC!) and it gets very hot quickly. I dont have any insurance, and since its been over a year I cant take it back to the store for them to fix it for free. So what can I do that doesnt cost a fortune?

(I am not very good with computers and technology, fyi) :)

Thankful for answers!