Greetings from South Africa

Hello everyone. I'm new to this forum and joined because I would like to improve my theory.

Currently I'm frustrated with chord construction. My guitar teacher tried to explain it but I just don't get it! Also I read up a lot and watched countless YouTube vids but still, non capisco. If anyone could explain it to me I would be incredible greatful.

So what I think I know so far, correct me if I'm wrong:

1. Can one build a C mayor chord on for example the 7th string. One has the c root note and then could one construct a note there? Or am I understanding it wrong