Framing the interior walls on a new home happens after the exterior walls are built and braced so they are straight. Interior walls are typically framed with 2x4 lumber. The most common framing layout for interior walls is 16" o.c.
The walls are laid out on the floor by looking at the plans to verify the wall locations. Mark the floor at each end of the wall. Measure over the thickness of the wall and mark the other side of the wall. Snap a chalk line between the marks. You now have the walls drawn on the floor. Mark the door openings on the floor, they will be transfered onto the plates later.
The top and bottom plates are cut and laid on the wall lines. Every plate should be the exact length of the marks on the floor.
The wall studs are nailed between the top and bottom plates. Then the walls are stood up and placed on their marks on the floor. The "double top plate" is installed after all the walls are in place, nailed to the floor and to each other. The double top plate firmly ties the walls together and makes the walls more rigid.
What else happens on this day
The roof trusses are usually delivered around this time because they will be installed soon after the interior walls are framed.