Target Acquisition is exactly that. The acquiring of targets through OPs, Drones etc. I think it also involves target analysis, such as for counter battery work. I admit, I am not the familiar with it, but I think it is a branch of field artillery.
As far as I know, when joining the artillery you can decide wither to be a bird or mud gunner. Their streams are different right up to Battery Commander. However, I have seen bird gunners being course officers on the FOO Tech crses, so there is some crossover.
Being an officer within the field artillery, your first jobs will be CPO, junior command post officer and recce officer. You work under the direction of the GPO. Once you become proficient, your next position will be GPO, where you command the gun position under the BK. By this time you should be a senior Lt in the Bty. From there you go on your FOO course and become a Troop Commander and FOO. Next is being the BK, and then BCs crse. In between you can take many other crses including staff crse, and potentially hold other positions within the Regt (such as Adjt or Ops O; both as a Capt). This is just a very brief synopsis of a Field Artillery Officer’s career progression.
CPO = Command Post Officer
GPO = Gun Position Officer
BK = Battery Captain, 2ic of the Battery
BC = Battery Commander