Concrete repair is considered a science and sometimes even tricky;
This is a brief guide on what product is best for what. Simply look for what you are going to do, whether it be "Crack Repair" or "Patch Repair" or "Protect Concrete", then find the right product(s) for any applications.
Once you choose the right product, go over to its page and read its instructions.
This page is right for a pro or a DIYer.
It's first important to know the crack size (width of crack). If you know the crack width, you ca choose the right product for you:
For patch repairs, it's about the depth, in which you need to apply the product., but more importantly, where it is being used: