
The most important bit of riding a bike is the bit where your feet and the pedals meet. Without a solid connection there, even the most highly specced and well-maintained bike isn’t going to go anywhere.
Much of the time, a pair of decent trainers or even some lightweight hiking boots will do the trick, especially if you plan on getting off your bike and walking around, but if you start to get serious about mountain biking, some mountain bike shoes are going to be on your shopping list.