What ever you call it that page does not explain HOW to use it.
The game uses confusing terminology at times. On browser, you click the scroll-like icon in the bottom middle of your screen. If you hover over it first it will have a tooltip that says 'Spells Inventory'. Everything in the 'Summonings' tab of that inventory is a building. They are earned as rewards in the game, crafted in the Magic Academy, or teleported into your inventory from your city (ex: I have teleported factories, workshops, armories, houses, etc over the years; that's where I'll find them later on when I want to put them back). Those 'summoning' buildings are placed in your city the same way you place buildings from the builder menu, but they only take 10 seconds to complete construction and do not require the use of one of your builders. You can hover over the bldg to get a tooltip that tells you their size and what resources (if any) it takes to place them.
It's a bit clearer on mobile, as they are under the 'buildings' tab. But, that tab is still located in the Spells Inventory menu, so first you have to know to look there. If you tap the building there, you get a page with the building listing the same info as the hover tooltip you get on browser.
In both places, the items players usually refer to as spells are under the 'Enchantments' tab. That's because the game called them 'Spells' for years before changing it to Enchantments.
Re-reading all that makes it sound about as clear as mud, lol! Please ask questions about anything you don't understand.