I'm wondering what you mean by see. That a being appears to you and is clearly there and speaks to you, or do you see some vague form out of the corner of your eye that is gone as soon as you look at it. If the latter, I would say it's nothing.
If they distract you from school or work or are accompanied with trouble eating or sleeping the visions mot be symptoms of a physical or mental illness or just a behavioral problem or active imagination.
If they are troubling rule out medical and mental causes. If they are not troubling live with them. If you are religious speak to someone in your religious community, an elder or a pastor.
If you feel compelled to do things that you suspect are wrong and this is associated with the visions seek medical help immediately. If no problem shows up there, consult your pastor right away.
A person can know many truths about God and other supernatural entities if he or she recites daily and with care the angelic psalter of the great Mother of God, Mary most holy.