use either word or open office.
without meing to criticise from the outset, if you don't even know that word, or notepad, wordpad even the dos edit program could be used to write a contract. (which is just a bit of paper). then I also doubt your ability to write a safe legally binding contract.
I suggest you have a solicitor, or other professional write your contract to make them safe
or you download a template and edit it.
or download a template to give you ideas.
I wouldn't suggest that you just start out with a blank page and write whatever comes to mind.