It is easy for those of us who learnt as children to say "its easy". I am sure that is what ski kids say when they see guys like me tripping over ourselves on the nursey slopes.
Teaching an adult is quite different to teaching a child to ride.
Do you have a bike at the moment?
There are a few fundamentals to remember when riding a bike?:
Bikes dont travel in staright lines, but a series of swooping curves. With experienced riders, the curves are so large that they appear straight, with beginers the curves should be more obvious.
You use the steering to correct for balance and change direction by leaning (much like flying an aircraft , which is no coincidence).
When you stop the bike with brakes, your body weight will continue forward unless you brace against the bars.

Find a safe place to ride, ideally a gently sloping grass field with a large run off area and no sticky-outy bits to ride into. Wear clothes to protect you from scratches if you fall. A helmet may be useful but on soft grass is not essential.
Start with the saddle low. Roll along and get the feel of stopping using the brakes.
Riding is easier if you go a bit faster, the bike will be easier to balance. Slow speed riding is quite a difficult skill.

Its really hard to describe a balancing activity in words, you just have to go and try it.