The bicycle is one of the most efficient machines ever made. A reasonably fit human on a decent road bike can move at fifteen miles per hour for hours on the energy budget of a couple of granola bars. The same person walking covers about a quarter of that distance on the same calories. That efficiency is the reason cycling spans so many uses and subcultures.
The main kinds of riding
Commuting. Short to medium urban trips replacing car or transit. The most practical use of a bike for most people. Any sturdy bike with the right tires works.
Road cycling. Drop-bar bikes on paved roads, mostly for fitness or long-distance riding. The category that includes the racing tradition.
Mountain biking. Wide tires, suspension, and bikes built to take a beating on dirt singletrack. Trail networks are now everywhere, including just outside most US cities.
Gravel. A newer category between road and mountain — drop bars, wider tires, made for unpaved back roads. Has grown fast in the last decade.
Touring and bikepacking. Loaded bikes carrying camping gear over multi-day trips. The slowest and most rewarding form of bicycle travel.
BMX and dirt jump. Small bikes optimized for tricks, parks, and racing on dirt tracks.
Picking a first bike
For most beginners the answer is "whatever fits, in good working order, secondhand." A used three to seven hundred dollar bike from a local shop will outperform a new department-store bike at any price. Get sized properly — a bike that does not fit will sit in your garage no matter how nice it is.
If you are sure you will mostly ride paved roads and trails, a hybrid or fitness bike is the most versatile choice. If you know you want to do longer rides for fitness, a road bike. If you plan to ride trails, a mountain bike with at least a front suspension fork.
Maintenance you actually need to know
Tire pressure. Check before every ride or two. The single biggest cause of flats is under-inflation.
Chain lubrication. Clean and re-oil every couple hundred miles or after a wet ride.
Brake pads. Replace before the metal backing touches the rim or rotor.
An annual tune-up at a shop. Cheaper than a new drivetrain, which is what neglected bikes need eventually.
Safety
Wear a helmet. Use lights front and back at all hours, not just at night — daytime running lights are the single best collision-reduction device after a helmet. Ride predictably and assume drivers cannot see you. Most serious bike-versus-car collisions involve a driver turning across the cyclist's path without seeing them, which is exactly what daytime running lights are designed to prevent.
BingBumpier