It means to speak to someone directly, sometimes with brutal frankness if necessary.
For example, instead of saying to someone, "Don't you think that dress is a little too tight on you?" If you wanted to confront her head-on you'd say something like:
"Get upstairs and change your dress immediately! You are not leaving this house looking like a stuffed sausage!"
It also means to get to the root of the problem, instead of fussing with the peripheral details. For example, if the roof of an office building is leaking, the company might put patches on it now and then to temporarily stop the water from coming in. Then one day the boss might say, "Let's just face this head-on and get a new roof installed."
- For Teachers