Questions about wordpress premium theme!

Hello guys!

I am a noob with WordPress,HTML,CSS,php etc.!

I bought a WordPress Theme (Vectors) and i want to make a variety of things to customize it!

Do i have to know html or css or php? I think css is the most easy of the three.. And i can make some changes from editor in the wp dashboard selecting style.css

In addition i want to know how can i change codes like html and php (where can i find them) and what knowledge should i have to change them?

Is anyone has a good tutorial for learning html/php/css ?

I’m waiting for your response! Thanks!