Can I still file my taxes for a tax return if I’m 18 and my parents claim me as a dependent?

Yes

It depends on your income. There will be an instruction book available sometime in the next month. Inside will be a flowchart that will tell you whether or not you need to file a return. Being claimed as a dependent doesn't absolve a person from filing a return. All that does is change your standard deduction amount. If someone else claims you as a dependent, then you cannot claim the standard deduction.

Yes

not unless you made under a certain amount

yes, and you might be required to file. You don't get a refund though unless you had too much withheld from your paycheck

Yes.

Yes. There is a box you check to indicate you are a dependent. Check to see if you really need to file based on your income and whether or not you had any income tax withheld.

You can if you are entitled to one.

Yes. Your standard deduction will be based on a formula. If you made less than $12,000 and had taxes withheld, of course you would file to get that money refunded to you. If you made more, the refund would be less (or you could owe).