If the framing is accurate, there's usually minimal shimming of each window - minor adjustments that align it perfectly in the hole provided. If needed, shims can be installed along any edge and from both sides of the window, with the two tapered edges of each shim meeting in the middle of the window's edge between the unit and the rough opening. Builders or window installers may shim before they caulk the opening.
Fastening a window to the frame may occur from the sides of the adjacent framing, or through a factory-applied nailing fin that extends from the edges of the window and is held tight against the outside sheathing to accept nails through to the wall studs. Often, the fin is flashed at the top before the installation of the exterior finish.
Once the window is secured to the frame, many builders will remove the sashes or unhinge the glass portion of a casement or sliding window that set them aside, protecting them from damage in a kitchen or bathroom.
Contractor lingo - condensation is the formation of water from air-borne moisture on a surface when temperature of that surface is below that of the air.