Since you've never done them before you can just take the very tip off for now - it'll be less traumatic for both you and your baby the first time
As for knowing where the quick is - I would cut just the tip off and look directly into the cut you just made - if you're nowhere near the quick it will look whitish - clip a tiny bit more till you begin to see a black dot in the middle of the whitish area, that is the quick. After practicing for a bit you will learn exactly how far into the quick you can go without making it bleed.
After trimming I go over them with a Peticure grinder just to smooth the sharp edges off.
Hope that's helpful