To answer your question, one doesn't get to choose spells. Each character has a predetermined list of actions/spells/abilities.
Each character has 5 unique abilities that are broken down into:
- 1 passive ability
- 3 "spells"
- 1 ultimate ability
The reason why I quote "spells" is that not all characters are magic users.
If you have auto level and auto items on (which it is by default) it will automatically level up your spells in the order HiRez (the game developer) has defined. You can override this order by unchecking autoleveling (which means you'll have to manually upgrade each level in game) or if you click on the "gods" menu you can define the auto leveling order.
The 2 abilities you were referring to are known as "actives". Think of an active as an item you can purchase that grants you a special ability. This special ability is on a cooldown timer. You have unlimited uses and once you buy an item you cannot sell it or discard. You only have 2 slots for active items.
You can view all items/armor/weapons/etc currently in game here: https://account.hirezstudios.com/smitegame/items.aspx I recommend sorting it by grid as opposed to list. (blue button, top right)
Please note that the game is still in beta and they do add/modify/remove items frequently between patches so make sure you read the patch notes after each patch.
Some of the items that are considered "actives" are:
- Aegis Amulet
- Creeping Curse
- Girdle of Might
- Hand of the gods
- Heavenly Agility
- Purification Beads
- Shielded Recall
I also have a small tutorial page at http://www.teamlqd.com/1/post/2013/11/smite-once-you-smite-you-know-its-right.html