People who try to start an exercise activity very commonly do too much their first time(s) at it, and end up injuring themselves or hurting too much which makes it hard to continue and even harder to start doing it again after they inevitably quit. The best thing to do is to start with something absurdly small - like biking a half-mile, walking (or running) 200 feet, or driving to the gym and then driving home without even going inside - and then very gradually ramp things up. The most important thing is to establish exercising as a regular habit, and then worry about turning it into actual physically effective exercise later on.