1) have you ever suffered that kind of situation?
"Have you ever been in that kind of situation?" or "Have you ever experienced that kind of situation?"
You don't suffer situations, although you may suffer through bad ones. You can suffer the death of a loved one, but situation is too general to used "suffer" with as it does not imply a bad experience.
2)Can you tell me something elaborately?
"Can you elaborate on that?"
"Please tell me about _____ in great detail."
The grammar of your sentence makes sense but the information does not. You don't ask that. You are not asking them to tell you anything specific, which doesn't make sense for a question. "Elaborately" is not used with questions unless you're asking someone to elaborate on some topic already mentioned.
3)what grade are you in?
Good. Just capitalize the first letter.
4) people who is working here get good pays.
"People who work here get good pay." better: "The people who work here receive good pay." (or a good salary)
People is plural, so you would use 'are' not 'is' - but you don't even need it in this sentence. 'The people who are working..." would be correct I think, but simply "The people who work..." is more natural. "Pay" is not used as "pays". Pay can stand for getting payed only once or getting paid multiple times (like a salary) depending on the context.
By the way, Can I use "now" behind the be verbs like I am now really tired.
Yes. I believe that is grammatically correct. "Now I am really tired." or would be a more natural way to say it though, or even better "I am really tired now."