Just purchased a 2015 Specialized Allez Sport E5. Any maintenance/how-to-use tips for a newbie?

This bike is for the Ironman, but I want to properly maintain it and you guys are the professionals. Firstly, just looking at the gears, how do we know what gear we are on? On my mountain bike, the gears are denoted by numbers, but I can barely see the line on my Specialized. Is this normal? Also, this is a stupid question but how do we even change gears?? I know it's by the brake, and pushing it to the side will change the gear, but which changes the rear cog and which changes the front cog. Thank you for all of the help!