I bought an iPad from somebody and they have it on iCloud lock and I don’t know the iCloud username or password

That iPad is on Activation Lock.

Without the information from the previous owner of this iPad, you will never, ever get this iPad working for you!

Apple will not get involved, either, since you are NOT this iPad's original/previous owner.

This iPad is dead to you.

If you can, return this iPad from where it was purchased and get your money back!