The "K" and hearts were not a stencil. :0) The white smeared a little is for a distressed look.
What you will need is tweezers, masking or duct tape, scissors, paint brushes or sponges, poster board or heavy paper, a computer, printer, Tulip Fabric Paint, Exacto knife or cutting tool, cutting mat/board/cardboard, cardboard or board for the shirt, spray glue (optional), and a t-shirt.
The first thing you do is wash and dry your shirt if it is new to remove the sizing in it. Now pull your shirt over a shirt board or a piece of cardboard so you can paint on it without it seeping through the layers of material.
On the computer pick a font and size that will work with the space between the shoulders of your shirt. Once you have the right words and font print it and trim off the excess edges. Now tape or spray glue it to your posterboard and cut out the lettering with your Exacto knife, razor knife, or scissors.
Trim off the edges, but keep at least 1 inch on each side of the words for a border.
Add tape to the edges so you can attach it to the shirt.
Using a paintbrush or sponge brush, dab the t-shirt paint onto the stencil's open areas. Press firmly on the stencil while dabbing it so you don't get paint under the stencil.
You will need to do between 2-3 coats depending on the color of your shirt vs the color of your paint.
Peel off the stencil. You may need tweezers. Be careful not to smear paint! Allow for drying time. We are impatient so we are speeding it up with a dryer.
Touch up any areas needing it. And dry again...
Cover the dried lettering with a towel and iron over the lettered area then wash it.
