Here’s a thread I started a few years ago about sts. I had questions. 
The video @Pigeonman links to in the thread from @Sebring is great. It’s really all you need for how-to make your own STS.
I think there are some links in there as well to ingredients available online.
As far as using it:
- Handle the chemical with care. Use PPE - gloves - eye-glasses + mask when spraying. Breathing in heavy metals is not a good thing. Wash your hands or any skin directly exposed to the spray when done.
- Cover the soil on the target plant before spraying to avoid contamination of the growing medium. A piece of cardboard with an “i” split for the stem works well and can be discarded after you spray.
- Keep the spray focused on the pre-flowering areas you want to reverse. Do this before “lights-out” and avoid returning a dripping target-plant to the grow-space in full-grow-light-power. Be careful not to get a wet-drippy sts-treated plant rubbing up against your girls. Let it dry before returning to the grow space if you can.
- Apply at least 2 x 5-7 days apart and in about 10-14 days you should see the staminate flowers forming.
- Store the leftover STS in an opaque-container in a refrigerated space and it should keep. I’ve used the same batch for 2-years with no loss in potency.
- Have a plan for disposal of the leftover STS if you don’t plan to keep it. Don’t simply pour it down the drain. It’s a heavy metal that can be toxic if ingested. Dispose of it as you would motor-oil or other chemicals/pesticides.
- Throw away the target-plant after he’s completed his work. Others may disagree, but in my opinion, do not ingest products of an STS (heavy-metal)treated plant. Your goal should be feminized seeds, not making concentrates or smoking IMO.