How is this done? Here is how I've learned to do it:

Find a Mandala that represents what you're trying to heal or meditate on. Place it before you and relax. Focus on the center of the Mandala. Stare directly into it, blinking as little as possible. Breathe slowly in and out. After a little while you will notice a shift - the colors of the Mandala will brighten and maybe even begin to move. Let yourself open to the energy pouring from the Mandala. Feel it flowing into and through you. Do this for as long as it is comfortable. After you see the colors shifting and pulsating for awhile, close your eyes - you will see an amazing thing! The Mandala will appear in front of your closed eyes. Watch and feel it as it pulsates - parts of the Mandala will brighten then fade. Imagine and feel the power and energy of the Mandala flowing through you. Feel it soothe and calm you. If you're trying to heal some part of yourself, feel the energy of the Mandala flowing into you - healing what needs to be healed. Repeat this for as many times as you feel you need to...