Your friend just started a work-study position in a biology lab. They are not really confident in their skills and are worried about doing something...

Your friend just started a work-study position in a biology lab. They are not really confident in their skills and are worried about doing something wrong. You've been trying to share what you've learned about biology. 

You've received a call from your friend. They've been asked to perform a PCR, they've designed primers, extracted the DNA, and are all ready to go but they seem to have misplaced their protocol (instructions). They need your help!

What reagents should they add to their PCR reaction and what does each reagent do? 

Note: Don't worry about quantities, just list what goes into a PCR reaction. Explanations for function don't have to be more than one or two sentences each. Revisit your virtual lab if you're unsure.