Tape down the vinyl paper on a cutting mat using a piece of masking tape in each corner. Tape the stencil down over the vinyl with masking tape if you aren't free-handing the design for your decal. Draw or trace your design on the vinyl with a pencil. Peel up the stencil, but leave the vinyl taped down.
Cut the desired design with a craft knife, following the pencil lines. Make your cuts long and smooth so the resulting decal has clean edges.
Separate the excess vinyl from the cut-out design. If the design consists of more than one piece, lay the pieces out on the work surface how you want them to appear on the wall with the vinyl side -- not the backing-paper side -- face up.
Cut a piece of transfer tape large enough to cover the design. Peel the backing paper off the transfer tape, then place the tape sticky side down over the design. Lightly rub the tape to adhere the vinyl to it.
Pick up the transfer tape, holding it with the sticky side facing away from you. Place the tape on the wall where you want the decal.
Working from left to right, rub over the decal with a credit card to adhere it to the wall while peeling back the transfer tape to the right to remove it from the adhered portion of the decal. Use a slight top-to-bottom rocking motion to help free the vinyl from the tape.