Part 1: Introduction
Part 2: Verb Forms
Verb tenses are probably the most difficult parts of English Grammar, especially for non-native English speakers and writers. There are two reasons for this difficulty. First, English has a lot of tenses, which express a lot of subtle information and emphasis about the location of events in time. Second, the labels applied to the rules for constructing verbs of the correct tense are profoundly misleading.
If you are a native speaker of English, you're probably using tenses very close to correctly, and if you make a mistake (especially in writing), the correction will almost always sound more correct than the mistake. Still, learning the actual rules is challenging. For non-native speakers, there are only two ways of learning verb tenses. The first is brute force: read a thousand books in English, and (if you're a hearing person) listen to professional productions (especially the news) on television and radio. (If you're Deaf, don't rely on Close Captioning for learning English grammar by brute force; the captioners make too many mistakes.) When you read and listen, pay very close attention to how the writers and speakers form their sentences. A thousand books is a lot of books, however, so the second way is to learn the rules. The rules are fairly complicated, and there are some irregularities, but there are fewer than a thousand books worth.
Some linguists and grammarians use "tense" in the narrowest sense, to mean only changes in the main verb to indicate time. In this sense, English has only two "true" tenses (present and future); the rest of the tenses in English all use auxiliary verbs, i.e. extra words that add time information. In this series, however, I use tense in the broader sense, to indicate all the forms of the complete verb, which includes the main verb plus all auxiliary verbs.
One of the ways that the labeling of verb tenses in English is that tenses have explicit time names (past tense, present tense, future tense, present perfect tense), and the serve to locate the verb in time, but these time names do not necessarily refer to actions in the stated time. For example, we can use the present tense to refer to actions in future time (the plane leaves tomorrow), and we always use the present participle to form the past progressive tenses (I was going to school yesterday) for actions progressing in past time. When you are studying the grammar of verbs, you must "free your mind" of the association between tense names and location in time. The names are totally arbitrary. In this series, I will always explicit add the word "time" or "tense" (or "participle") to be completely clear.
Tense is only one aspect of verbs. There is also voice (passive and active) and mood (indicative, imperative, and interrogative) for main verbs. Additionally verbs can be used in place of nouns and as complements to other main verbs (notably the gerund and the infinitive). I will cover these other aspects of verbs in a different series.