Can you tell me in order to meditate must one quiet the mind completely and make it think nothing except om or visualizing a certain object?

Focus on your breath: It's difficult to quiet the mind completely. Many thoughts and feelings flood one's brain. What works for me is to close my eyes and focus on my breathing, taking deep slow breaths. As thoughts or feelings emerge, imagine breathing them away. You may want to begin meditating for a few minutes at a time and gradually engage for longer periods.