I don't quite understand arrays and pointers etc

Question

Hello, I just finished the lesson on data types, arrays and pointers and I feel like I still don't really understand them. I mean I now know a definition of a "pointer", a "double" or a "float", but I still feel like I don't know what they are good for or what they would do in an actual program. Can someone give me some more examples of when these functions are important?