how to secure computer from unauthorized use?

[Allinlife]

so basically im moving to dorms tomorrow (yea kinda late, but realized commuting is not the way lol)

gonna be moving my computer with dell 30'' monitor

I obv don't really want anyone to open up my PT or login to my poker sites.. i know it's a thin shot but i'm not willing to take any risk.

what are some safe methods to only allow computer for my own use?