Time has to do with our movement through space and events. Time is an inescapable corporeal experience. There is a past time that has already been traversed. There is a present time--fleeting though it is--during which we consciously function, for example, presently listening to music, thinking and typing. There is a future time that can be imagined and is anticipated and may hold the unknown about which we may think and for which we may plan and work but which is as yet unmaterialized.
Tenses are linguistic constructs that allow language to conveniently refer to the inescapable corporeal experiences of the movement of time--the movement through space and events.
In English, tense is liguistically indicated by inflection, which is the addition of endings to verbs to indicate specific representations of time. English has two tenses, past and present.
Futurity is indicated in English in two possible ways. The first way is by the combination of the modal verb will with the base form of an infinitive verb: will + sew (to sew). The other way is the combination of present (tense) progressive (aspect) with an infinitive verb [be + -ing participle]. The auxiliary verb be is used in its is/am/are forms: is/am/are + -ing + infinitive: He is, I am, you are sewing.