Here is a definition of TAC-P, it is an American one, but the description pretty much sums it up. What is not mentioned, but is a fact(unless recently changed) people going TAC-P come from a Weapons background not IFR or VFR so if you wanted this you would need weapons training and quals first:
"On a battlefield, they form a tactical air control party team that plans, requests and directs air strikes against enemy targets in close proximity to friendly forces. A TACP is generally a two-airman team, working in an Army ground unit and directing close air support firepower toward enemy targets on the ground"