- Summoning. When I try to cast "Summon familiar" nothing happens. I have the correct amount mana - am I doing something wrong?
When you select a summoning spell, you need to cast it on a tile (your mouse should change to a casting cursor and when you mouse over tiles they should highlight green if the spell is castable on that tile.
- Enchanting. Same goes with giant strength. Again, nothing happens.
Similar to Summoning, this needs to be cast on a unit on the map. There's some funkiness to casting on a stack, so you might want to break off the specific unit and move it to its own tile, cast the spell, then stick it back into your army. Your Sovereign should get an Enchantments tab next to Stats/Abilities which will show all the enchantments he's maintaining (Familiars/summons go there, too).
- Food. Okay, so my cities can't grow without enough food, and there are no natural food resources nearby - what are my options?
Find some 
Not much else to it than that. You should always start by one fertile land, which will let your city grow probably to level 3 or so. Once you have a few cities, you can research trade to get caravans, which greatly boost the food production in the cities they're trading between. There should also be research in the Civic tree to increase the food income from farms by a percentage, and this research is repeatable.
