'Tab' and 'shift-tab' are just two ways of IDing the enemy you want to target. 'Tab' will cycle thru all targets in view, similar to the check6 function, you just stop hitting tab when you highlight the correct target. 'Shift-tab' will auto highlight the centermost target in your LOS, Line Of Sight.
In the TA , just hit 'Ctrl-Tab' to highlight friendlies, offline you need to enable the LCG in FlightModeFlags as mentioned.
When you get into FlightModeFlags, hit the 'Change' button to see your options.