Those are VERY general questions you're asking..
but the colorful beacons are "COMMAND POINTS".. the cp's that your team controls are green and the oppositions are red. the goal is to capture as many cp's, which bleeds the "reinforcements" (score at top of screen)...
colored bars? not exactly sure what you're talking about, but you might be referring to your health...
enter/exit vehicles - default key is "e" but can be changed in Options->Control... I suggest you take a look at your options to familiarize yourself with the different keys and their bindings.
To use the jetpacks, press the jump button twice (default space bar)
You can respawn as many times as you want as long as your team is in possession of at least one Command point (green beacon)
but continue playing SP and this will become easier for you to understand.. have fun
feeling froggish? leap..