How does one who catches up with the congregational prayer in the third rak'ah complete his prayer, and does he recite Al-Fatihah and a surah in the remaining two rak'ahs, or only Al-Fatihah? And what is the meaning of performing actions without recitations and vice versa?

The preponderant opinion is that whoever catches two rak'ahs of the 'Isha prayer should, after the Imam's taslim, stand and complete his prayer with two rak'ahs reciting only Al-Fatihah, based on the understanding that what he caught with the Imam constitutes the beginning of his prayer.