Food is one of few sources in game. When you feed dinosaur you level up them (you know that before).
Every high level give you more coins, so if you want quicker level up your dinosaurs you can have more coins and coins are second important source in game. You can buy food by cash. How much you have to pay it depends of how much do you want have food. The other way to get food is start production in dedicated building for that. Unfortunately it cost. You have to pay coins to unlock production. In level 1 it is 600 coins and you activate production 5 minutes long. You can collect food before end this time but only a part food. You can upgrade your buildind but you have to be on level 5. You can ask: what for I need food? Of course for your big pets 😉
You need coins for example produce food. The second reason is for buying buildings like acu security office or decorations like fountain. If you don’t want buy a new dinos you can always evolve those which you have. Every building gives you coins. You can collect also coins from your farm with dinos. Every farm gives you some coins. For example farm with Triceratops gives you xxx coins per 5 minutes but each level up your dinos (you can have more than one dino in farm) and more dinos gives you more coins per 5 minutes. Look: triceraptos on level 3 and on level 16 gives me 140 coins per 5 minutes. When I level up to level 4 my second Triceraptos it will give me 144 coins per 5 minutes. So, when you level up your dinos you have to spend coins (for food) but later your investment will be paid but you have to be patient.
DNA you can only get from 3 ways: once is by selling your dinosaur, second is buying by cash (in panel it looks like a real money) and the third way is by watching free advertising. I thing watching advertising is the best way to get free DNA. Why? Because you can use Jurassic World The game cheats or Jurassic World The game hacks but watching a video is more simple (and you can see something what will interested you). You need DNA if you want buy Dino from market.
Last source in Jurassic World The game is cash. Cash is extra source which with you can buy everything and you can make everything. You can buy cash for real cash or you can get it for free when you make a few thing (for example install another free game like Clash of Lords 2). When you made it to get cash. If you don’t want install you can buy for real money. It is easier way but if you really want play this game an be a champion it could be good decision. If you need more coins for buying food or buildings you can it buy paying cash. Also if you need food you can buy it. So if you want always have multi source in game (cash is multi source because you can buy everything by that) you have to buy a cash!