if I use tactical retreat on a unit does it do its full damage before being sent to base and does it conquer

Yes, it deals its full damage — but no, it will not conquer.

Tactical Retreat doesn't send the unit to base right away. It only sets up a replacement effect for "the next time it would die this turn." So the unit stays at the battlefield, participates in the Combat Damage Step normally, and deals its full combat damage simultaneously with the defenders. Only afterwards, if it took lethal damage and would die, does the replacement effect heal, exhaust, and recall it to base instead.

It won't conquer, though. Control and Conquer are determined during the Resolution Step, and that only happens for the player who still has units remaining at the battlefield (Rule 466.5). Since your unit is back in your base, you have no units there (assuming it was your only one), so the defender establishes or keeps control — and they may even conquer if they haven't scored that battlefield this turn. If you had other units still present, those could conquer, but not the recalled unit.