I'm new here and have no idea how to use it ..
I have a lot of questions to ask
Welcome to the PF.
It looks like you figured out how to make your first posts in the QM forum, but I'll give you a couple tips anyway. Under INFO at the top of the page, there is a link to the Help/How-To page. That page has lots of useful info on how to post here. Also, it helps to post as much information as possible when starting a new thread. Post links to the reading you have been doing so far, and give as much context to your question as you can. That makes it easier for us to try to answer your questions.
Also, when you have schoolwork-related questions, post them in the Homework Help section of the PF, and fill out the Template that you are provided there.
Also, your equations will be easier for everybody else to read if you learn how to use LaTeX:
The symbols on the palette above the message-editing box are OK for simple equations, but people will appreciate it if you use LaTeX for complicated ones.
Separate names with a comma.