Learn Finnish: Olemme valmiita menemään virtuaaliselle areenalle.

This sentence sets up the context for an action rather than commanding it; it says "We are ready to go" instead of "Let's go". If you wanted to use the formal 1st person plural imperative taught in this lesson, you would say Menkäämme virtuaaliselle areenalle! (Let us go to the virtual arena!). Just remember that in everyday speech, Finns almost exclusively use the passive form mennään for "let's go".

Why does "ready to go" translate to valmiita menemään instead of using the basic dictionary form mennä?

In Finnish, the adjective valmis requires the verb that follows it to be in the third infinitive illative form (-maan/-mään). While English uses the basic infinitive ("ready to go"), Finnish expresses this as being directed toward an action, translating literally to "ready into going".

Why is valmis in the partitive plural (valmiita) rather than the nominative plural (valmiit)?

When describing a plural subject (implied here by olemme, "we"), predicative adjectives describing human states, conditions, or emotions usually take the partitive plural. Olemme valmiita is the standard grammatical way to express that a group of people is ready.

Why do we use the allative case (areenalle) instead of the illative (areenaan) for going "to" the arena?