implementing paypal payment system problem

hello, my website is available at
the website is in hebrew so there might be a language gap, even so - my problem is - i cant seem to figure out how to embed the members paypal payment system for users to pay for an account. is this done by changing certain settings and by so changing the register form? is that done by pasting a shortcode into a certain page? i can't find my answer by far. your help will be appreciated. thank you.