Here's the short version...

First, you need the drug's formula. Do the RP requirements to get the formula for a drug (see the chart in the main rules). You can reduce the RP requirements if someone else with that formula gives you access to it, or if you use up one dose of the drug.

After this, you have the formula. You can make that drug.

Then, you do the RP requirements for 1 dose of the drug. Halfway through, make an Int/Level/Luck roll. If you make it, then finish your RP and you get a dose of the drug. If you don't, you can stop right there and start on a new dose if you want.

You can reduce the RP requirements by paying some of the cost or by using a Drug Lab. You can get bonuses to your roll by doings more RP.

You can overdose if you take too many doses in a day.

You can also get addicted to the drugs if you use them too frequently too often, and you'll be taking penalties until you get un-addicted.

Healing Powder: Mix 1 part Xander Root, 1 part Broc Flower, 5 paragraphs of RP, and an Int/Level/Luck roll. Shake well. If you make the roll, you get a Healing Powder.

For more details and reasonings, please read the longer version of the rules.