Media quieres - what widths to use?

Hello,

I have been learning about responsive design lately

My problem is, I don't know for how many and which widths to adapt my websites for...
I have been reading, people say to do these: max-width 320px, max-width 480px and max-width 800px

I don't know if those are enaugh.. and for how many widths do you design, which ones do you use?

It all depends on the specific site you are creating since each site has different elements that you must work within. Your question is really impossible to answer. Responsiveness is based upon need. If you don't need to change any elements to fit the screen at width 800px, then don't

By the way... 320px would be older-style mobile phones.