Bracing is an action to ready a weapon, so it can be fired without penalties.
From the corebook (p. 127):
Heavy weapons always require two hands and must be braced in some way, usually either on a bipod or tripod but equally it could be a windowsill or sandbag (or the firer’s shoulder in the case of RPG launchers), to be fired without penalties.
These penalties are descripted few lines above, on Heavy Weapons:
Firing a heavy weapon without bracing incurs a –30 penalty to hit and prohibits Semi-Auto and Full Auto fire.
With the exception of the Lascannon (Heavy) and Laspistol (Pistol), all Las weapons are Basic, which do not require bracing nor gain any benefit from the Bracing action.
Can I “brace” with an Integrated Weapon?
If it's a Heavy Weapon, yes, you have to use the Bracing action or take a -30 penalty to hit.