Hi, I was trained in linguists, not English, and these are called “verbs”. It is impossible to make a full sentence without overt use verbs in English. For example, in English we say “It is hot.” But in Russian you can say just “hot” (zharka). The “It is” is implied. English translates that one word into three. We a “strict” SVO word order (subject-verb-object) that occurs 99 percent of the time, like Danish and Norwegian (though not German which technically has a verb last rule where the verb originates on mental level and then move to the second position is there is no helping verb). Another weird fact: English has only two verb tenses. The verb can transforms into “could” as a conditional tense and can be used to indicate future time (I could go there). While “will,” the main way to indicate future action, is actually a verb occurring in the present tense and is followed by Ann infinite to indicate future. “I am going to eat lunch” is also a statement about future action that uses present tense verbs. “I could go”, “I might go”, “I’m gonna go,” I want to go” indicate future action with present tense verbs, sometimes in the conditional form.
English teachers probably don’t know that fact. Your teachers were wrong. The linking verb is the actual verb while the verb following it is a participle, like “going” and in the previous example, or a noun or adjective as in the “hot” example. The use of “it” is merely a place holder not indicating or referencing anything. Tense is a state of verb, while future action is a frame of mind referenced to by other construct. (Don’t worry, Chinese Mandarin has only one verb tense.)