The Living Room fireplace is a sealed gas unit with remote control. That makes it super simple to use, when it works.
From the remote, pressing the "ON" button (looks like a 0 with a 1 overlaid on top of it) will cycle through the modes of Thermostat, fixed level, or ON-Max. The up and down buttons will then allow control of the set temperature. It should be pretty easy to understand, but if not, consult the manual. If the fireplace doesn't turn on, even when set to MAX, the first think to check is the batteries.
If the remote control is not sitting out and visible, it probably means that we have taken the batteries out of everything so that they won't discharge and leak (which happens in just a few weeks time). In this case, the remote will be under a panel at the front of the fireplace. The batteries will be there with the remote. There are also batteries for 2 other system components. One is the valve controller part of the system which will have the battery pack of 4-AA batteries disconnected at a connector - this needs to be reconnected. The second item is a "remote receiver" that also takes 4-AA batteries. Also check that the gas valve is open - fully counter-clockwise and aligned with the pipe.
If you have trouble getting the fireplace to turn on, one debug step you can take is to move the switch on the remote-receiver to the ON position.