You can buy thermoplastic in different ways, the most common are small beads (Jett Sett) and sticks (Thermo Loc). The products are different, the beads are heated in water and the sticks are heated with a heat gun or microwave or other heat source. I use the beads and simply add them to hot water, let it stand, the beads start to melt together and become translucent and pliable.
It is hot when you pull it out, it can be carefully moulded into whatever shape you need. You can keep dipping it in the hot water to soften the plastic until you have the desired shape. To recycle just pop it back into hot water and it will become pliable again.
Each product will have information on the best temperature and method to soften the product. Thermoplastic does get hot so you need to be careful handling it. I use a spoon and a glass jar that I only use for this product and not for food. If you are making handles or steel tools and are using thermoplastic softened in water be careful to dry the tools thoroughly to prevent rust.
Pic 1: Thermoplastic beads ready to put in hot water
Pic 2: Thermoplastic used to fix a bracelet front to a dowel to make stone setting easier
Pic 3: Thermoplastic used to make a custom handle to a handmade bezel rocker.