Can anyone help me with her aggresive behaviour (sometimes)?

I recently found this stray cat (around a month ago) and decided to keep her with me. Now I need some tips to take care of her, firsly I want to determine how old she is to get her vaccinated properly, secondly I want to know abou the potential diseases she could have that are transmittable and third - she meows (screams) alot when I'm with her or not with her, I keep her in a seperate room for now because our house is kind of open so she can easily escape... What should I do to keep her calm. She's also hyper active and sometimes attacks my hand. Most of the times she freindly and sleeps on my lap but sometimes she gets aggressive so how can I improve that?