It helps if you get him familiar with the brush first. Maybe spend one or two minutes a day, just with him on your lap or where ever you plan to groom him. Stroke the back side of the brush down his back, if he stays still, praise him. Touch him with the brush, just a few little strokes. Touch his feet, belly, ears etc.
Brush very gently as just pulling on their hair can hurt these little guys. I always hold my hand at the base of the hair (at the body) so not to pull away from the skin, and I pull the hair through the brush towards the body, not pull the brush through the hair away from the body. if he does have matts or a matt, start by working it apart with your fingers, try some Cowboy Magic on it. Then hold the part of his hair that is closest to his skin and work out the matt from the end of the hair strand, so you are not pulling his skin.
Most important: keep praising him when he lets you brush him, love on him, tell him what a good boy he is. Do a little each day, maybe not even ten minutes yet. Try doing two sessions of maybe 3 minutes in the morning and 3 minutes at night. He is still a baby, it will take some time.
Be patient, consistent, and persistant. REWARD and PRAISE and before you know it, he will be enjoy (or rather, he'll pretend to enjoy, lol) his grooming sessions
