〜ます

〜ます is the polite-register affirmative non-past — "do X" or "will do X" in polite speech. 食べます = "[I] eat / will eat." It's the form taught first in nearly every Japanese textbook, because it's safe in any encounter with strangers, teachers, customers, or coworkers.

The conjugation point: ます attaches to the verb's i-form (連用形), not the dictionary form. For ichidan verbs drop る (食べる → 食べ + ます). For godan verbs shift the final う to the い-row (書く → 書き + ます, 飲む → 飲み + ます). Irregulars: 来る → 来ます, する → します.

ます conjugates as a self-contained auxiliary: ません (negative), ました (past), ませんでした (past negative), ましょう (volitional — "let's"). The verb stem before it never changes once you've identified the i-form.

ます is register, not tense or politeness level in the strict sense. The plain-form counterpart 〜る / 〜u carries the same temporal meaning; the choice is purely social. Native speakers fluidly switch between ます and plain forms based on relationship to the listener.