The game itself is Free to play, though most people I know (not me, since I don't have the cash) have bought Google/IStore cards to transfer over and use in the game, You can't PVP each other, though you can make friends with people you know (this is explained in guides).
The basics of the game is that you form a team of Servants to level up and beat the story. One Servant is automatically given (Mashu) and can't be removed, since she's vital to the story. Then you have a free gacha roll, where you get 10 out of a bunch of cards, whether they are Servant cards or Craft Essence cards (these boost your Servants' stats and give various effects). You then get some Free Servants and CEs, to start playing.
There are two types of gachas mainly, with some event specific ones now and then for the events. One is for Saint Quartz, which is a type of limited virtual currency you can get through completing the story or using money to buy them, and you get an assortment of the various Rare Servants and Craft Essences (ranging from 3* (can reliably get in a SQ roll) to 5* (very rare and requires several rolls, with people often losing a few hundred dollars in getting one specific 5* Servant)).
The other is the Friendship Points gacha, or the F2P one, where instead of SQ, you use Friendship Points, gained by using your friends' supports, and isn't limited. You however can only get the common Servants and CEs, going from 1* to 3* max.
This is all available whether you use a phone or emulator, since it's part of the game itself and comes when you download it on the phone/emulator.
