If you are referring to the accessory drive belt located on the front of the engine the general procedure is to relieve tension on the belt by first finding the belt tensioner, then using the appropriate tool to push it in towards the (usually) center of the engine and then taking the belt off best way you can. It isn't really hard to do this. Reinstallation is a little harder. Follow the diagram which will be located somewhere under the hood, and you can't go wrong. Of course you will also have to push the tensioner aside to put the new belt on.
( Yes ) the 1999 Ford Explorer has a serpentine belt It is used to " drive " the accessories Power steering pump , alternator , etcetera
Your Explorer has a serpentine belt tensioner which keeps the proper tension on the serpentine belt unless the tensioner has failed.
The explorer has a timing chain, not a belt.
On one of the stickers in the engine compartment , ahead of the radiator , there should be a serpentine belt routing diagram
That's the accessory drive belt at the front of the engine for your power steering , air conditioning compressor , alternator etc.
A loose belt on the motor.
The Ford Explorer engines use a timing CHAIN
The 1999 Ford Explorer has a cam chain not a belt. No maintenance is required.
I believe the Explorer does NOT use a timing belt, but rather a timing chain
The 2001 Ford Explorer Sport V-6 has a timing belt. Ford engines have not use a timing chain since the 1980s.
The belt turning the alternator which is recharging the battery.
near the belt