All you need to get started is
here[
^]. I, and others, am curious as to why you don't want to go via paypal's site. The reasons to do it far outweigh any reason not to. If you openly show payment is via paypal then users will be given an added level of confidence. If you try to hide it and ask for their credentials then the majority of people will smell a rat and decide NOT TO SPEND ANY MONEY WITH YOU.
Best advice - use paypal as intended and reap the rewards.