Free servants?

"Free" servants can be referring to either one of two things:

• The free 3 star servant at the end of every "order" or chapter of the story line. (IE: Fuyuki gave Caster Cu Chulainn at the end of the order)

• The event servants that are awarded during select events (aka welfare servants). More often than not, there's a lot of grinding that comes with gaining one of these servants... but they're well worth your time.

As for your second question, the best way of farming mana prisms in my opinion is to do the 40 AP exp quests and burning all the exp cards (of course this is saying that you have your servants maxed out and have no need for exp cards in the first place). There may be better/more efficient methods, but this is the only one I know of.

Every time you clear an order you get a free 3* Servant. For Fuyuki is Caster Cú, for example. They appear in your gift box, just in case you haven't noticed.

You should already have gotten caster cu, if you don't have him, check your present box, and he should be there. You get one each story map/order you clear

to get mana prisms, the fastest way is to grind the 30 ap exp quest, and burn the cards you get, as each one gives you one prism. To get quartz, just going through the story is the best way for you right now, and later doing interludes and free quests once you're done with those.