Formatting means prepare your disk to be usable by your software system
Devices using different software systems ( pc, smartphones, cameras ecc..) are usually able to read/write only a limited set of "formats" and may not be able to use others
So you must check on your device instructions which type of formatting your disk needs to be usable by that specific device.
Usually cameras and video recorders have a function to format the inserted card in a way they like (check the functions menu).
Remember. Format WILL ERASE every data on your card !