Draw the desired crease lines across your rectangle.
Select any number of adjacend faces and then apply the ‘Rotate’ tool on that selection. Position (and first click) on the crease line to get the faces rotated (folded). When first clicking, do not let go of the left mouse button, but drag the ‘Rotate’ tool along the edge that represents the crease line, to set the rotation axis. Then let go of the Lmouse button. Then second click (starting point of rotation) and third click (end of rotation). You can now even enter a rotation angle (degrees) and hit [Enter] to establish a fixed rotation.