In combat, one team mate may ‘Help’ another willing ally:
Help
You can lend your aid to another creature in the completion of a task. When you take the Help action, the creature you aid gains advantage on the next ability check it makes to perform the task you are helping with, provided that it makes the check before the start of your next turn.
Alternatively, you can aid a friendly creature in attacking a creature within 5 feet of you. You feint, distract the target, or in some other way team up to make your ally’s attack more effective. If your ally attacks the target before your next turn, the first attack roll is made with advantage.
The Question I have is: Can this be used as a bonus action, or used whilst concentrating on a spell?
If something can be performed using a bonus action, it is always explicitly stated in the description. The lack of such a statement indicates that it can only be used as an action.
Concentration is only broken by specific things, which are listed on page 203 of the PHB and are:
Casting another spell that requires concentration (*)
Taking damage
Being incapacilated or killed
(*) Readying a spell or casting a spell with a casting time over 1 action also requires concentration (PHB 193 and 202, respectively).
Taking the Help action is none of these and thus will not interfere with concentration.