Every available AT&T booster works similarly: the signals coming to and from your nearest AT&T tower are amplified by the booster.
The basic structure is explained in these two graphics:
Every AT&T signal booster has three main parts:
An outdoor antenna that communicates with the tower.
A signal amplifier that's "bi-directional" - that means it boosts the signal both the "uplink" and the "downlink" paths.
An indoor antenna that that communicates with the tower.