We can move and fold out large structures because in space there is very little resistance. On Earth when we want to move or articulate large structures, we must work against several forces. In space we only have to contend with mechanical friction.
In a microgravity environment, such as in orbit around Earth, objects are effectively weightless. This means we don’t have the mechanical strain of moving a large object in opposition to gravity. A great example of this was the doors on the Space Shuttle cargo bay. The motors powering these doors were not powerful enough to open them down here on Earth, but they were more than adequate to do so in the microgravity of low Earth orbit.