It matters on how complex your design is. If it is just a couple, place and then press it. If you are making a more elaborate design, build it on a piece of wax paper with low track adhesive, then use a piece of transfer sheet to move it to the garment. Press and let fully cool before removing transfer sheet. If a stone pops up, just place it back by hand and repress. Once all are on the garment, flip and heat from the backside, the makes sure you fully heated the glue into the garment.
For others following this thread not you Chris, heat press stones are not permanent for t shirts and other wearable. They are known to come off in the wash. The best way to have them last through a washing is to hand wash and hang dry.