Just to give some example, imagine Modern Warfare 2:
For assault-rifles, you have the M4A1. For Pistols the Beretta M9. Both are extremely accurate with a mediocre fire rate.
For assault-rifles, you have the F2000. For Pistols the USP45. Both have a very high rate of fire but aren't that accurate.
For assault-rifles, you have the FAL. For Pistols the .44 Magnum. Both have extremely high damage outputs and good accuracy, but can't be fired as fast as full-autos.
For assault-rifles, you have the SCAR-H. For Pistols the Desert Eagle. Both aren't very accurate, but have a high fire rate and good damage output.