I want to learn about variables or different command lines using man (man) command, but i can't

Question

I am using hyper termianl in my windows laptop and i don't know how to use ( man ) command which is manual for learning about variables.

Please tell me if there is any different command for manual or learning about variables

I tried to learn about (echo ) command using (man) but my terminal telling me BASH: man is not defined ;