Cycling has a low barrier to entry compared to most active hobbies - most people already know how to ride a bike. The parts that actually trip up beginners are less obvious: bike fit, road awareness, and pacing yourself so the first ride doesn't end in sore knees and a bike left in the garage for a year.
A bike that's the wrong size causes more discomfort than almost any other factor, including the bike's price point. Seat height should let your leg nearly fully extend at the bottom of the pedal stroke with a slight bend in the knee. Most bike shops will do a basic fit check for free, even on a bike you didn't buy from them.
Cycling uses muscles differently than walking or running, so a distance that sounds easy can still leave you unexpectedly sore. A 20-30 minute ride on flat terrain is a reasonable starting point for building the specific endurance cycling requires, rather than jumping straight to an hour-long route.
Ride predictably, signal turns with hand signals, and assume drivers haven't seen you even when you think they have. These habits become automatic quickly, but they matter most on the very first few rides when they haven't yet.