Click on the empty tiles to the left to construct buildings, use them to defend your base from enemy and to produce units to attack them. All structures are upgradeable, which makes either them or units they produce more powerful.
A Soviet soldier taking part in the Battle of Stalingrad in 1942. To purge the city from the invading fascists, you got rifle, grenades and you can call backup. Make use of the reinforcements at your disposal.