HOW to increase my endurance with cycling?

You want to check your tire pressure first. You want to do an easy 10 min warm up and then start pedaling at 70-90 rpms at all times. Select a gear that is easy to pedal but gets you breathing to the point where you can still talk but not sing. You want to ride for distance don't worry about the speed. Work your way up to a hour or more. Hills and the wind can make a huge difference and a mountain bike on the road is not very efficient.