Make sure you wear gloves and a mask when handling.
You must weigh it with an accurate milligram scale.
Let's pretend I weigh out 10mg of fentanyl, I would then do the following.
To then accurately dose, dissolve it in 10-100ml of either a saline solution, or sterile water.
Close the lid of whatever you are keeping the solution in, and aggravate it for a minute. The fentanyl should be visibly dissolved already, but to be safe, shake again once every 15 minutes for another two hours.
You now have a fentanyl solution that is simple and accurate to dose.
If you used 10 ml of water for your 10mg of fentanyl, you now have a 1mg (1000ug) / 1ml solution. This can be ideal for injecting, just pull up 10ccs (0.1ml) of solution, and you have 100ug dose of fentanyl, equal to 10mg of morphine in potency. Inject how you wish, but make sure you were very sterile when making the solution and keep it in a cool dark place.
If you used 100ml of water for 10mg of fentanyl, you now have a 100ug / ml solution.
1ml (100ug) is equal potent to 10mg morphine. Good for oral dosing, sublingual, intranasally (slowly dripped into nostril) or plugged.
Be very cautious and smart with fentanyl. It can kill you easily.
Dose small at first, triple check your math and the accuracy of your scale when making the solution.
Don't expect as much euphoria as oxy or h or anything, this can lead to chasing a euphoria that fent can't be achieved and will just lead to severe respiratory depression.
Again, I can't stress enough, use your head when around this stuff for real.
Good luck.