There are several choices for this level, and they depend on what you did in the previous level. If you chose Poland-Gdansk or Poland-Bialystok, then you can now play Germany-Hanover or Germany-Dresden. If you chose Belarus, then you can now play Ukraine (which is identical to Germany-Hanover!).
To play Germany-Hanover, choose the north arrow. To play Germany-Dresden, choose the south arrow.
The two missions are similar. In both cases, you start with a small force, have to fight your way to a damaged, partial friendly base, fight off continual enemy attacks, and eventually wipe out the enemy base. However, the Dresden mission is a lot harder than the Hanover one, primarily because your base exits are further separated and thus harder to defend, and Nod has a lot more tanks and uses them to attack, while you only get 2 good anti-tank units. You will need to know where your base is before you start, especially in the Dresden mission, otherwise you won't get there in time, or you will get wiped out before you get there. In the Dresden mission, your base is on the south map edge, and is reached from the SW map corner. In the Hanover mission, it is in the SE map corner.
Dealing with the Nod tanks
There are 3 methods that make sense. Anything else is madness.
1) You get 2 medium tanks. They can beat large numbers of the Nod light tanks without further attention from you. But they do take damage, and if you lose them, you could be in trouble.
2) Large numbers of Grenadiers. You may think that blowing up tanks, even light tanks, by having infantry stand in the open and throw grenades or satchel charges or Molotov cocktails or rocks at them is madness, and in real life, it is. However, in C&C, large numbers of Grenadiers will reliably beat the tanks as long as the tanks do not overrun. If the tanks do overrun, kiss your infantry good-bye. Using this approach requires excellent micromanagement, and you pretty much have to ignore the rest of the map while the one combat is going on.
3) Blocking the fords. There are multiple choke points (river crossings) near your base, only 2 of which need to be guarded at any given time. Park an APC (or Humm-Vee) on the choke point, which blocks it completely. Now your Grenadiers can stand behind the block and throw their bombs and be safe from overrun. This method is costly, but at least your casualties are replaceable. Most importantly, this method requires very little micromanagement.
Special: free cash
In these missions, you can find a crate containing $2,000 on the map. Just touch the crate with a unit to get the cash. In the Dresden mission, the crate is north of your base, across the river, hidden behind a deciduous tree. You cannot find it by visual methods. Either you stumble across it by accident, or someone told you to go there. In the Hanover mission, the crate is near the river fork.