Help explaining set and interval notation

I’m a grade 10 in Canada and absolutely lost when it comes too these in graphs, I somehow managed to get the correct interval notations on my last test but I still don’t understand how or what they are.

I’m a grade 10 in Canada and absolutely lost when it comes too these in graphs, I somehow managed to get the correct interval notations on my last test but I still don’t understand how or what they are.