Regarding verb-subject agreement in English, let me add that in addition to adding -s for third person singular in the present tense, there still is the somewhat defective conjugation pattern of the verb TO BE with its variant forms according to subject and the verbal tense system:

TO BE - am, are, is - was, were

Anyway, compared to other languages with full and more complex verbal conjugation sets, there is only a minimum in English and should be easily mastered even by beginning English language learners after they have come to understand the structural principle of subject-verb agreement as part of a verbal conjugation system in English and other Indo-European languages.