Hi, When you step into battle circle there is one movement and then another to set your wizard in fighting stance. One can't get into the crown shop on the first slight movement. Wait for the second. Go to the crown shop BEFORE you cast any card quickly and all the way right to find henchmen. Very little time to do this so check out the crown shop before a fight so you know where to find a henchmen and what one you would like. I have found level 50 henchmen for 50 crowns each very helpful. The level 50 life is great at keeping your health up and all on your team so you can concentrate on damage. The level 50 fire is good as is the level 50 death( uses deer knight and scarecrow). It depends on the school that you are fighting. I tried the level 50 ice but wasn't thrilled. It kept using taunt which I think is a waste of pips as I don't see that that spell does anything. I haven't tried any other henchmen. If you cast a card the crown shop will close. The henchmen go away if you flee or are defeated. When you return to the battle you can pay to get them again.
Do you mean there are no Henchmen on the pages when you open the Crown Shop? That happened to me also. Unclick the "Useable" button. That should open up your possibilities. Then you can follow all that advice in the other answers.