Lay the canvas down on a flat surface with a towel or other material underneath to protect the artwork from damage.
Insert the pointy end of the canvas keys into the slots located in the corners of the frame. Each corner will have two keys. Place the long side of the key flush against the frame. Some canvas frames come with the keys pre-installed.
Press the keys into the frame using your hands. Try to place the same amount of pressure into each key around the frame to avoid buckling the canvas.
Check the tightness of the canvas. If the canvas is tight no further adjustment is needed. If the canvas is still sagging place the canvas back on the towel face down.
Place a small block of wood flush against the back of the key and hit the block with the hammer. This protects the key and canvas from any hammer damage.
Continue pressing the keys into the frame until the canvas is tight.