Powdered herbs can be used to make tinctures in exactly the same way as chopped herbs. It’s upside is that the surface area is greatly increased so more extraction can happen. The downside is that they tend to hold more tincture when pressing so it is good to have a solid tincture press or something similar to retrieve as much of the resulting tincture as possible.
The other method you can use with powders is percolation, but this has a whole set of specific instructions and is best demonstrated as well. However I would encourage you to look into percolation to see if it interests you since it is a much faster way to make tinctures, but more involved too.