I couldn't figure out how to use the portals, I tried having enemies walk on them and placing it under soul but no luck.
I enjoyed the mechanic of having the enemies use the souls of their fallen comrades to get stronger, nice touch!
Oh hey, sorry about that! I guess I should've made it more clear. Once you place a portal down, you can right click on it to place a soul if you have any (indicated by the count on the top right).