ٱلَّذِينَ يُقِيمُونَ ٱلصَّلَوٰةَ وَيُؤۡتُونَ ٱلزَّكَوٰةَ وَهُم بِٱلۡـَٔاخِرَةِ هُمۡ يُوقِنُونَ
Who establish prayer and give zakah, and they, of the Hereafter, are certain [in faith].
They are those who establish prayer properly, give zakah, and believe in the Hereafter with certain knowledge.
They do not merely pray; they establish it. That is, they keep prayer standing as it deserves by making it an unshakable pillar of their lives. Mindful of the welfare of society, they also fulfill the obligation of zakah.
But notice the emphasis placed on their relationship with the Hereafter:
وَهُم بِٱلۡـَٔاخِرَةِ هُمۡ يُوقِنُونَ
And they, of the Hereafter, are certain [in faith].
The pronoun هُمۡ (they) is repeated here to reinforce the emphasis. Their conviction about the life of the Hereafter is not merely an ordinary belief.
It is يَقِينٌ (from the same root as يُوقِنُونَ), that is, an absolute certainty that guides every decision they make.