Paper is jammed and cannot
It can vary a lot from one printer to the next, but I suggest this . . .
Turn off the printer at the mains supply (you really do not want it grabbing your fingers inside) :)
Look down the back where the paper gets taken in, and see if any paper is visible in there, if so, carefully remove it, you may have to use some long handled pliers or grips of some kind.
If it all seems clear, the paper jam may be a bit further inside the mechanism. Inside there are several rollers that grip & guide the paper sheets through, and this is where paper is usually stuck.
Open the printer lid (not the scanner, but the whole lid as if replacing the ink cartridges. And check carefully nothing is hiding in there. Most paper is white and so easily visible, but some gets ink on it when jammed and may even be black and near invisible in that dark area.
Be very careful to not damage any of the mechanism inside, as they are usually very sensitive to things being poked around in there.
If after all this, no paper can be found, you may need to take the complete lid off the printer to get right inside, which is a bit of a bigger job.
Also, unless you are 100% sure that it is paper blocking it up, unplug all cables, and gently turn the printer over to see if anything falls out :)
I fix printers as an engineer, and have found, coins, pens, biscuits, sweets, paper, labels, pencils, a sandwich!!, toys, hair ties, elastic bands ! Never found any small animals in one yet, but there's always tomorrow :D
Good luck with it.