It's not always possible to spend a lot of time on hand-sewn repairs. In such cases, iron-on patches can be perfect for a quick fix for a hole or a stain.
The flowers are sold individually.
Although they are designed to be ironed on as they are, I recommend also sewing them on if you have the opportunity, as it will be much more durable. However, you can iron them on quickly first if needed, and then sew them on at a later time.
It's easiest with a sewing machine since the iron-on patches are stiff, and it might be worth using a darning foot if you have one, and then removing the feed dogs, so you can move the fabric/garment in any direction you want. Feel free to practice on a piece of scrap fabric with a ballpoint pen drawing of a heart or star or something. The stitches don't have to be perfectly even; the most important thing is that the patch is securely attached :)
Iron-on patches are a bit stiff, so if it's a very large worn area with a small hole, I would recommend attaching a reinforcement patch to the inside of the garment first, either with machine stitching (a bit like quilting with stripes or squares, perhaps with thread that matches the garment?) or by using a fabric patch and Vliesofix, and ironing it on the inside, and then covering the hole or stain with the flower. Of course, you can also use iron-on patches to decorate clothes that don't have any damage or wear yet :)
Reinforcing worn areas on the inside is beneficial to prevent a new hole from forming right at the edge of the iron-on patch, where there will be extra stress from the hard patch against the thin/worn fabric.