I love verbs. Verbs are strangely complex, partly because of our diverse history of stealing words and tenses from other languages and partly because English has more tenses than first glance (it's not just present, past, future).
What does tense mean? Let's start there.
Verb tense in an English sentence generally shows two things: 1) agreement with the subject and 2) time.
Starting with subject-verb agreement, at its simplest definition and without considering irregular verbs, means that a singular noun takes a singular verb (which typically does have an -s on the end), and a plural noun (with an s) takes a plural verb (which typically does not have an s).
Basic subject-verb agreement rules start with the premise that if the noun has an -s, the verb does not, and vice versa.
Of course, this gets waaaaaaay more complicated. Let's take a look at two.
1) Prepositions or modifiers:
2) Single numbers:
Each and every are considered "one," so when words like these are used with a noun (even more than one), the verb is singular. For example,
Google subject-verb agreement or check out the Azar Grammar books--the third, blue book has a great section on complicated subject-verb agreement.
Funny thing: you may see people flinch at sentences like "Each of the teachers who help the team get a bonus" or "Everyone of the students are ready," but like many rules in grammar, the numerous infractions of these rules seems to make these rules more flexible.
Game on. Bend the rules.