If you describe something as visible, you are saying you can see it. Certain things are not visible to the naked eye, but that doesn't mean they are invisible, you may just need a microscope or telescope to see them.
The adjective visible also means obvious to the eye. You'd use this sense if you want to point out obvious flaws in an object such as a car with visible dents and scratches. A third meaning for the adjective is easily available or accessible: You may try to be a visible presence in your kids' lives — although sometimes they would prefer that you blend into the woodwork — so that they know they can count on you and come to you with any problem.