A copy and paste from Boeing 777 FCOM in 2 parts:
In flight:
Push (after lift-off with takeoff reference thrust limit displayed) – • removes takeoff and climb derates and assumed temperature thrust reduction • A/T in HOLD, activates A/T in THR REF mode • disarms LNAV and VNA V, if armed • between 50 feet and 400 feet, selects TO/GA roll mode • above 400 feet, selects TO/GA roll and pitch modes
*Annunciations are: • THR – autothrottle applies thrust to maintain the climb/descent rate required by the pitch mode • THR REF – thrust set to the reference thrust limit displayed on EICAS • IDLE – displays while the autothrottle moves thrust levers to idle; IDLE mode is followed by HOLD mode • HOLD – thrust lever autothrottle servos are inhibited. The pilot can set thrust levers manually*
I hope this helps somewhat! Will find the link with respect to take-off!