I want to set up Time Machine for my Macbook pro but I already have files on my seagate hard drive. Will i lose them if i set up time machine on it ?

So i have a 2 TB Seagate time machine. I had an older laptop that I had transfered things from onto that about 2 years ago. My current macbook has been acting up so i want to set up time machine. Will i lose everything on the hard drive if i try to set it up as time machine now?

I read about partioning it.. but Im still scared i will lose what is on it?

My macbook is about 2 years old running OS.X 10.9.1

Please advise.