I would suggest if you are new to cycling and unfamiliar with bicycle mechanics taking it to a shop and have it tuned. ask about replacing the chain and freewheel. it my cost a bit more than doing it yourself but if the bike is runing well you will enjoy riding it more. you have lots of time to learn to work on it.
perhaps there is a fellow BFer nearby wo is willing to help.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk