It varies. I tend to see F2P games as broken up into two (somewhat subjective) categories: Free to Win and Pay to win.
Pay to win means that punitive XP level grinds are common, necessary loot and characters are behind paywalls, and generally a game structure set up so that you will have to pay at some point or leave.
Free to win doesn’t have any of that, but while still a micro transaction game, it is balanced and relies more on users wanting to customize their experience or throw money back to the devs because of the rich experience they’re getting. Items that you can buy don’t imbalance a game for someone that didn’t buy them; but allow you access much, much quicker or pimp out your experience (think how home sells avatar clothing).
Planetside 2 sounds more like the latter, where customizing weapons\vehicles and getting XP gaining perks is the main focus of the paid items. Maybe someone who has played on PC can give a better overview.
As to how they make money? Some do some don’t, but ultimately it relies on making a kickass game. Due to the low barrier to entry (free to play) many, many, many more users will at the least download and try it. If they can get someone hooked with a great experience, they’ll probably drop some change into the game at some point. That they can reach so many more people, they make up in sheer numbers with low cost digital goods.
It’s somewhat the app microtransaction model, but more applied to a full game experience with the better ones not segregating the communities they build.