help me with robots meta!

Let me start by saying im new to this so be easy…I’m having difficulty figuring out this whole robots META tag. i have a website that im trying to SEO but ive reached a wall with this. I need to know what “no follow” means, i cant seem to get a clear answer or get one in dummy terminology.
lets say i have a page for every product i promote should i have it set to index,no follow? or should i just have one page and a new post on each product?