Hello I need to check if my laptop has warranty
The screen is black and I have no idea what happened
Question marked as
How old is the Mac, i.e. what year is it?
If it's more than one year old the one year warranty has expired. Unless you elected to buy the extended warranty, that coverage is also not available.
You can check coverage here: Check Your Service and Support Coverage - Apple Support
The serial number is on the bottom of the Mac in very small faint text. A magnifying glass is a big help reading it.