Can you help me troubleshoot a 2000 Craftsman, 6. 75 HP, 21" Multi-Cut Power Propelled Rotary Lawn Mower which has developed an oil leak and a pretty good one to boot?

I am a little green on 4 Cycle engines and hope someone can help me out. I have a year 2000 Craftsman, 6. 75 HP, 21" Multi-Cut Power Propelled Rotary Lawn Mower which has developed an oil leak and a pretty good one to boot.