Using Broker questionFollow

I made some spells that I wanted to sell via the broker located in the crafting guild.However, he won't take it. I click on sale and try to deposit the spell in one of the spell slots to no avail. I keep geting the message that I have to put the item in a container first. What container and where can I get it?

Bottom line: How do I use the broker to sell stuff? I must be an idiot.