Definitions of basic commands

My name is Jorge Luis, i´m from Perú, i´m a new student, I’m getting a little difficult to understand everything, since it’s a completely new topic for me.
I basically want to learn how to program and be able to develop my business ideas.
So far in the little that I have advanced I have been using the commands of the videos, but I would like to know and understand why of each of them, is there any site or can someone provide me some help regarding this information?
Thanks a lot
Jorge Luis
Wapp: 952064840

Let’s start with a specific command that you might have. Pick one and we can start there.

For example, if i want to develop an app from the beginning, what is the first command i should use?
What dos it mean “sudo gem”…?
Thinks like those, i do not understand the meaning of each