Sadly there's not some magic way to move your creatu from your showroom to your shop.
To move them to your shop assuming they are already on your profile, click the "Stock Pets" button on the Rancher Shop page and then you can check the boxes of the creatu you want to put into your shop.
If the creatu you want to put in your shop are currently in your showroom, go to your showroom, click "Edit Stock", select the check boxes of the creatu you wish to remove from your showroom, click "Remove". Then, go to your Rancher Shop, click "Stock Pets" (same as earlier) :)
And then in your Rancher, to give your creatu prices, you'll need to click the "Edit Stock" button, enter the prices for each creatu, and click "Save"
Hope this helps!