New driver

i just got a 95 impala with overdrive and i was wondering if i should put it in overdrive all the time or is there certain times to put it in OD or regular drive? and will keeping it in overdrive cause the transmission to slip?

Read the manual. You will want to put it in overdrive for normal stop and go/highway driving. It provides the best fuel economy. You will want it in drive when you are either on hilly surfaces, or towing something.