If I understand your question, “Let’s ...” is the first person plural imperative. I would say “let’s get started” in a situation where I was with a group of people and I wanted us all to start doing something. “Let’s” is also a contraction of “Let us” but it’s extremely rare to hear “Let us get started” though that would mean the same thing.

If I understand your question, you want to know what the alternative to the passive voice is. The opposite of the passive voice is the active voice. Active voice is when the subject of the sentence is the one directly "doing" its verb. Here's the same idea conveyed in passive vs. active voice: Monkeys love bananas. (Active) Bananas are loved by monkeys. (Passive) In the active version, the verb agrees with "Monkeys"—you're directly saying how the monkeys feel. In the passive version, the verb agrees with "Bananas"—you're explaining how the monkeys feel by describing a quality of the bananas. Passive voice is useful when the object being acted on is the actual focus of your writing rather than the thing or person doing the action. It can also be useful when only the result of an action (rather than whoever or whatever did the action) is known: "Three cows were decapitated on three separate farms in Stockton yesterday, but police are still unable to say by whom." In general, though, it's best to use the active voice since it's often more concise and easier to understand.