Car Code Question? p0420?

i have a 1998 ford explorer and i the check engine light came on. I took it to auto zone for a diagnostics and it gave a code for P0420. Bad catalytic converter, engine misfire large vacuum leak and engine oil leakage into exhuast-valve i really don't know what any of that means so my question is. Is there anyone out there who has experience in this stuff that's had this happen to them and if so plz tell me the cost, most likely problem