There are different flavors of dog toothpaste and special dog toothbrushes to make things easier. Under no circumstances should you use human toothpaste.
Dogs do not know how to spit it out and the fluoride in the toothpaste is not good for them.
If your dog is an adult, brushing may take time and practice. To begin with, make the experience fun for him and be patient. It might be a good idea to put a little toothpaste on your finger and rub it on his teeth and gums to get him used to the taste. Spend as little time as possible doing this at first, as your dog has never had this done before and if you spend too long he might resist.
After a few days doing this you can try again, this time with a little toothpaste on the toothbrush. He will enjoy licking it off and after a few more days he will be used to the taste and will allow you to begin brushing. It would be better to be consistent and practice daily.
Praise him very often and don't try to hurry this new experience for him. Once he is relaxed and sitting, gently pull back and lift his upper lip so that he looks as though he's smiling! Brush just one or maybe two teeth for a few seconds. If he resists it would be best to stop and try again the following day. If he is OK with this, continue gently brushing more teeth.
Don't expect to brush them all in the first attempt! Repeat the next day, gradually extending time spent on each tooth, stopping after a minute or so to praise your dog. Even though he loves you it will be a natural instinct for him to resist until he has time to overcome any fear and allow you to proceed.
If brushing your dog's teeth is too difficult, there is now a way to clean the teeth with either a gel or spray. Whichever you choose is whatever you feel is easier to apply. Both the gel and spray get rid of plaque and bacteria when mixed with your dog's saliva.