Once my cousin showed me this thing that would make your guy fight monsters automatically. You would select a lvl or monster and it would attack all surrounding you. Any idea?

Yes that's called an autofighter.

The best one out there is called 'SCAR'. You can download it at SRL-Forums - SRL Homepage (http://www.srl-forums.com)

It has these things called scripts, which are made by SRL members on the forums. To find a script you want, register, get 10 posts, and wait a week so you can browse scripts. Then go to the 'Junior member scripts' forum and go to the category of macro you want (In your case you would go to the Fighting section). Then you can look through the list of scripts and find the one that works best for your need (Usually you'll want to look at the highest rated ones).

Good luck, and try not to get banned!

I've seen the auto fighters too, but never knew how to get them. I quit playing Runescape a little while ago, but my brother still plays. I should tell him.