Objectives: 1) Fix the ruined bridge with your workers, 2) fight the enemy, and 3) conquer all enemy TC-s.
Hint:
Once you are on the other side of the river, try to build towers to defend yourself.
When you have killed all the enemy units, occupy all enemy buildings (move your unit into the enemy TC to occupy it) .
The more workers you have to help build a structure, the sooner it will be ready.