Quality control: selecting samples created by a method, measure/test the attribute you caring about, compare the result with the specification, and if you measure deviation from this specification make an adjustment directly or indirectly on the parameter(s) which have an influence on the attribute you care about. It is an active control thing. Buy construction supplies after checking their quality.

Quality assurance: it is a broader concept. Generally, how do you assure that the process will give you the outcome you desire? You can achieve this by defining the specific task to be done during the process, or actively control the process by sampling it from time to time. Get the best quality construction supplies from a construction supply online shop.

For example:

You want to renovate your house. You have a concept about how should it look like in the end. How can you assure that after the renovation you get the results the closest you wanted at the beginning? First, you think about what do you want. But to be able to remember later and to be able to communicate to others you write them down.

Now you have to hire some people to do the job you want. How do you do it? Do you hire the first person who told you he can do it, or take a more cautious method? These are the kind of things that QA cares about. Now you’ve found your person, who starts to work. How do you assure that he does his job properly? You check his work from time to time against your agreement and kick his ass if it deviates from it and makes him correct his work. That what the QC is about.