Gwent has three different in-game currencies
- Ore (represented by a small stone icon)
- Scraps (the green scroll icon)
- Kegs (represented by the barrel icon)
To earn ore, you’ll need to start playing games. As you win matches against non-AI players, your progress bar will creep higher, and at various increments, you’ll receive rewards. These are typically either Scraps or Ore, though they can be card kegs as well. Win more games, get more money. Also, at the end of each match, both players are given the option to send their opponent a Good Game, and this GG comes with a gift of either 5 Scraps or 5 Ore (you will get this reward only if the opponent sends a GG)
Ores are used to buy kegs which is the Gwent equivalent of card packs. One keg can be bought for 100 ore.
The green scroll icon represents Scraps, which is another type of currency in the game primarily used for card crafting which is done in the Collection section of the game. Crafting is unlocked after you reach level 3. It is presumed that you get scraps as you disassemble duplicate cards. You can also earn scraps by playing the game. Players will be able to buy Scraps with real money via in-game purchases. Amount of scraps you need to spend depends on the rarity and quality of the card you want to make. Better the card means you need more scraps.
Keg icon shows you how many unopened kegs you have. Each keg rewards you with 4 random cards and then you get to choose the fifth card from three that are offered. As mentioned earlier kegs can be bought by spending 100 ores or with real money.
NOTE: I couldn't find the exact amount of ores/scraps you can get. I will edit this answer if I am able to find it.