The previous advices are good, I will add to get two toothbrushes, one for you and one for him. Let him play with the water of the sink and his toothbrush, while you are brushing his teeth. This helped me with my 22 months old.
About the tooth paste it really doesn't matter if the tooth paste has fluoride, even if the child doesn't spit it yet. What it is important is that you keep it out of his reach, so he can not eat it any other time of the day. But just swallowing pea-size tooth paste twice a day it won't harm him, just find one that he like the taste.