Questions & Answers about Пойдём внутрь.
Пойдём is the 1st person plural future form of пойти.
- пойти = to set off, to start going
- пойдём = we will go
But in sentences like this, Russian often uses this form to mean let’s go rather than a plain future we will go.
So:
- Пойдём внутрь. = Let’s go inside.
This is a very common Russian way to make a suggestion that includes the speaker.
Not in the strict grammatical sense.
Russian does not usually use a special imperative form for let’s ... the way English does. Instead, it commonly uses the 1st person plural future form:
- Пойдём. = Let’s go.
- Посмотрим. = Let’s see.
- Поедем. = Let’s go / let’s drive / let’s travel
So it functions like an imperative in meaning, but grammatically it is a future-tense verb form.