Why not start walking locally.
Start by walking round the block a couple of time, then gradually extend the walk to include a local park, then do more roads, more parks, staying out longer each time, and build it up like that.
Once you have got used to walking then jog for short sections, gradually increasing the amount you jog.
DONT go at it hammer and tongs from the start or you will soon get fed up with it.
DONT join a gym as many people who join a gym get fed up after a while and stop going but still have to pay for their years membership.
Maybe go to the GP for a check up before starting your keep fit regime.