Expanding is basically enlarging your base to close or remote locations. Expanding can be used to secure Ore Nodes, Tech Structures, or to set up a forward base. It is common to expand your MCV, build some structures, and then pack up and move somewhere else. All units that are used to expand have no weapons and must be protected from enemy attacks.
The Allies can expand with their Prospectors. The Prospector deploys into a Command Hub, which gives a larger buildable area than the Soviet Sputnik, but takes more time to deploy, and is more vulnerable to attack. Each Command Hub must also be upgraded individually.
A safer and less expensive strategy is to repack the MCV itself and move it to create a new base elsewhere on the map. When moving the MCV, placement of production structures must be kept in mind at all times of the game so that technology can be used to the most effect.
The Soviets expand with their amphibious Sputnik vehicles. They unpack into Outposts, which give less buildable area than Allied Command Hubs, but unpack much more quickly.
With the Crane structure, the mobility of the Soviet MCV can be brought into the picture. With the crane as the major build queue, the MCV can move along the map deploying only long enough to place scaffolds with the crane before moving along. This provides Soviets with the fastest potential to expand among the factions.
Empire of the Rising Sun
The Empire has the easiest way of expanding thanks to their Nanocores, which can deploy almost anywhere on the battlefield. However, because the Nanocores cost more than the other factions' refineries and must physically move to their destination from the MCV, they are also the riskiest expansion method, especially when the expansion locations are far from the MCV.
Nanocores are excellent for taking Ore Nodes. Remember to send at least one Defender Core to protect against enemy Terror Drones, infantry and light vehicles and aircraft. More Defender cores may be needed if the new base site is in an exposed or high-traffic area. If need-be you can switch the Defender between targeting land units and air units. It can be a good idea to have a contingent force of Nanocores on standby to set up a base expansion, in case your original one is destroyed. All structure Nanocores, however, have a small ground control around them once deployed, which makes building perimeter walls difficult. Furthermore, each new factory you build has to be upgraded individually, which hinders you from pulling out high tech units from front line factories too easily.