1996 Honda Civic is leaking oil, why an how do I fix it?

I have a 1996 Honda Civic EX Coupe, automatic, 144k, an its leaking oil. Whenever I start the car it sometimes hesitates, I read on some of the forums that mean that I have to replace a ring seal. Is this true? an if it is how much does it cost to replace or is it something I can do by myself?