Make sure you use bac water
The volume of water you mix with will determine the concentration per ml
So first. How many ui's of hcg do you have?
If for eg you have 5000ui's
1ml of bac water will give you 5000ui/ml
2ml of bac water will give you 2500ui/ml
5ml of bac water will give you 1000ui/ml
Then you can use the insulin pin to measure how much if that you need and pin.
As for mixing. Make sure the water has been refrigerated first as temperature can destroy it. Also when putting the water i to the vial don't just squirt in directly at the powder and do not shake the vial to mix it either. What you need to do is once pin is in the vial,tilt the vial and pin so that you can slowly add the water drop by drop hitting the inside wall of the vial and the dropping into the powder. Once the volume is injected it should be pretty much mixed but you can give the vial a little gentle whirl to ensure its all dissolved in the water. Once again do not shake.
Does that answer everything?