AoS Getting back into the game and need some clarification

I am returning to the game after a 20 year break and am quickly trying to catch up on everything. I am doing lots of converting of old models to round bases right now, or putting models on bases for the first time ever (yay 3rd edition models).

I am seeing lists that say 1 drop or 4 drop. What does this mean?
For the summon spells, do you have to deploy this troop for the mage to know this spell? Or, do the mages know the spell because it is in the army manual?
Can you summon out of dead troops or should I have extra units at the ready to summon?
When I start a game, Can I look at my opponent's roster? Any advice on quickly learning what I should care killing first or avoiding?

I'm excited to get back on the field, but am feeling a bit overwhelmed by all the information I need to know to get playing again. Thanks!

 

Welcome to the forums!

Summoning is not done with spells anymore, it is a special ability of army that a Slann can use. There is a list in the Generals Handbook what you can summon and how many summining points it will cost. Slann generate those points by sacrificing spells instead of casting.

About drops:
units are placed on the battlefield before the game. The players alternate placing them. Those are the drops. Bataillons allow placing some or all of their units in one drop instead separately.
So for example if you play a Shadowstrike Starhost (a bataillon consisting of two units of Skinks, a Starpriest and 3 Terradons), a Slann and an Astrolith Bearer that is a three drop list while without a bataillon that would be 6 drops.

And Yes, before a game you can take a look at your opponent's roster.

For starting the game I recommend getting the new core book and generals handbook.

 

Is there an advantage to having fewer drops?

 

I think whoever finishes dropping first gets the choice on who takes first turn

 

Yep, that is the main advantage.