CAN A BAD FUEL PUMP CAUSE OTHER THINGS TO GO BAD ON MY 2000 FORD EXPLORER SPORT?

WHAT DOES IT MEAN WHEN ITS SAID YOUR SYSTEM IS TOO LEAN

Change the fuel filter first… Cheap and simple… A dirty fuel filter can impede fuel pressure and cause the system to run lean.
Had it happen on my '96 Explorer Sport.

Yes, and so can keeping your caps lock on.

Yes, it can. Too lean means too little fuel entering the cylinders.