Θα περιμένουμε στη στάση μέχρι να έρθει το λεωφορείο.

Θα is the particle that marks the future in Modern Greek, so Θα περιμένουμε corresponds to we will wait / we’ll be waiting.
It’s not a standalone verb; it combines with the verb form that follows. Depending on context, it can express simple future, intention, or prediction.

Greek doesn’t form the future by changing the verb ending into a special future tense. Instead, it uses Θα + verb.
So περιμένουμε is the present-tense form of περιμένω (I wait), and Θα + περιμένουμε gives we will wait.

περιμένουμε is 1st person plural: we wait / we are waiting.
With Θα, it becomes we will wait / we’ll be waiting.

στάση is in the accusative after σε/στη in Modern Greek.
Many location expressions use σε + accusative to mean in/at/to depending on context. Here it’s location: at the stop.

Not always. στάση literally means stop and can be used in other contexts (a stop on a route, a pause, etc.).
But with λεωφορείο right after, στη στάση is naturally understood as at the bus stop.

μέχρι means until. When it’s followed by a verb, Greek normally uses μέχρι να + subjunctive.
So μέχρι να έρθει... literally works like until (that) it comes... → until it arrives.
If μέχρι is followed by a noun/time phrase, you don’t use να (e.g., μέχρι αύριο = until tomorrow).

έρθει is the aorist subjunctive form of έρχομαι (I come / I arrive) for 3rd person singular: (that) he/she/it come(s).
Here it refers to το λεωφορείο (the bus), so: until the bus arrives.

With μέχρι να, Greek commonly uses the aorist subjunctive to mark the arrival as a single completed event (the moment it comes).
A present subjunctive would sound more like an ongoing/process meaning and is less typical here.

λεωφορείο is neuter, so it takes the neuter article το in the singular.
Greek normally uses a definite article where English might omit it, especially for specific, expected things in context—like the bus you’re waiting for.