How to view the values ​​in the variables of the running process?

Question

Debugging

Actually, it became interesting: imagine there is a process, let it be exe, let it still use dll, how can I see the contents of the variables?
For example, the same calculator - there is a variable where the number is stored,
For example, the same icq chat - there is a variable where there is a message text,
how to look at them in memory?