A long verse. In this post we'll look at the introductory phrase, and a question.
οἳ καὶ εἶπαν Ἄνδρες Γαλιλαῖοι, τί ἑστήκατε ἐμβλέποντες εἰς τὸν οὐρανόν; οὗτος ὁ Ἰησοῦς ὁ ἀναλημφθεὶς ἀφ' ὑμῶν εἰς τὸν οὐρανὸν οὕτως ἐλεύσεται ὃν τρόπον ἐθεάσασθε αὐτὸν πορευόμενον εἰς τὸν οὐρανόν.
The first three words include the first verb:
οἳ καὶ εἶπαν
Εἶπαν - 'they said' - is a common form, used over 90 times in the New Testament. It is the 3-P, aorist active indicative of . . . well, let's call it λέγω, as εἶπον is often listed as the third principal part (a second aorist) for that verb.
The subject is οἵ, referring back to the two men in the previous verse. This word can be thought of as a relative pronoun ('who said') or a personal pronoun ('they said'), depending on how it is rendered in English.
Then, a question:
Ἄνδρες Γαλιλαῖοι, τί ἑστήκατε ἐμβλέποντες εἰς τὸν οὐρανόν;
The capitalization of Ἄνδρες is by convention, indicating the beginning of direct speech. In this case, the two men are addressing the apostles.
Γαλιλαῖοι is often, but not always, capitalized as well. Γαλιλαῖος, Γαλιλαία, Γαλιλαῖον is an adjective ('coming from Galilee, person of Galilee'), and the capitalization is by the same convention that gives us 'Minnesotan' from 'Minnesota'.
Τί introduces the question. Τίς, τί, with an accent, is often an interrogative pronoun ('who? what?), but when introducing a question it can also be used adverbially, to mean 'why?'.
The accent on τί never changes to the grave. Without an accent (τις, τι), the same spelling is used as an indefinite pronoun.
There are two verb forms in the question. Ἑστήκατε is 2-P, perfect active indicative of ἵστημι, 'I stand, I make stand'. Note that the rough breathing in principal part 1 translates to the rough breathing in ἑστήκατε, indicating that the initial ε is not an augment.
Bλέποντες is a participle (masculine plural nominative, present active of βλέπω, 'I see') and completes the action introduced by ἑστήκατε:
why do you stand (ἑστήκατε) looking (βλέποντες)
The final part of the question is a straightforward prepositional phrase, explaining where the apostles are looking: εἰς τὸν οὐρανόν, 'into the sky'.