Here's the entire verse again:
οἳ καὶ εἶπαν Ἄνδρες Γαλιλαῖοι, τί ἑστήκατε βλέποντες εἰς τὸν οὐρανόν; οὗτος ὁ Ἰησοῦς ὁ ἀναλημφθεὶς ἀφ’ ὑμῶν εἰς τὸν οὐρανὸν οὕτως ἐλεύσεται ὃν τρόπον ἐθεάσασθε αὐτὸν πορευόμενον εἰς τὸν οὐρανόν.
The two men have addressed the apostles, and asked them why they were standing there, looking into the sky.
The rest of the verse is still fairly long, and I am splitting the analysis into part 2 and part 3. Note, first, that it is continued direct speech from the two men to the apostles, and that there are four verb forms, indicating reasonably complicated remarks.
It might help to break this part of the verse into short phrases:
οὗτος ὁ Ἰησοῦς
'This (the) Jesus' - all in the nominative, so it will need to be the subject of something. English does not use 'the' with proper names; koine Greek sometimes does, and modern Greek almost always does, exceptive for the vocative.
ὁ ἀναλημφθεὶς ἀφ’ ὑμῶν
We have another two nominatives. The masculine singular article ὁ refers back to Jesus but also forward to ἀναλημφθείς, connecting the two.
Ἀναλημφθείς is the masculine singular nominative form of the aorist passive participle of ἀναλαμβάνω, 'I take up, raise up'. So Jesus was raised up ἀφ’ ὑμῶν - 'from you', the 'you' indicating the continuation of direct address.
εἰς τὸν οὐρανὸν
A straightforward prepositional phrase - 'into the sky / heaven'.
For some reason, English says either 'into the sky' (singular, with article), 'into heaven' (singular, no article), or 'into the heavens' (plural, with article). In this case, almost all English translations use 'into heaven', thus following the number of the Greek (singular), but not the presence of the article.
So far we have something like:
"this Jesus, who was taken up from you into the sky"
The remainder of the verse will be covered in part 3, together with a translation of the whole.