Javascript on WordPress?

I have a free account, and I have Google Adsense and I want to be able to put a little block of Adsense in, but I don’t know how or where I could put that in. Its a free account, so I can’t really edit the page itself. I tried putting it in a text sidebar widget, but that didn’t work well. I really don’t know what to do, I’m raising the money to be able to buy a host to be able to use WordPress on, but I can’t unless I get the money, unless I put ads on the site… where could I put them? Is the only place in the actual entry itself, or will that even work? All help is appreciated.