viens is not plural, even though it has an "s" at the end. It is just the first person (I) present tense of the verb venir. It can be confusing and an easy mistake to make at first. Many first person singular (and second person singular ) verbs end in "s" because that is just how the word is spelled. The verb agrees with its subject. The plural pronouns, we, you (more than one or one formal, and they usually don't end in "s". I hope this helps a bit and I am sure someone else will have a better answer. Just hang in there and it will get clear.
