To begin, the game gives you an introduction and takes you to catching your first Magikarp. Once caught, it will stay in your pond, which can be decorated. Food will fall into the water and you can tap on one to get your Magikarp to eat it. This will increase it’s JP, but you can also train it. Training doesn’t require input from the player, Magikarp will train on its own.
There are also other Pokemon in the game, which often offer support. You can obtain some by playing, but you can also use some of the game’s currency to buy new ones. I have a Pikachu and Piplup that I acquired by progressing through the game. I also have a Litten that I bought with in-game currency. When they get an exclamation mark above their head, I can click on them to get various bonuses. They also appear during jump battles and provide additional support.
Each Magikarp is limited by how high it can level up. Your first one can only get to level 11 or so. As you progress in the game and gain experience, your character’s rank will go up, which will allow you to catch Magikarp that can level up higher. Their higher levels allow them to have more JP. Once you reach a Magikarp’s max level, you’ll need to finish a league and (win or lose), your Magikarp will retire afterwards. Then, the game lets you catch another one.
There are a variety of random encounters that can occur. Some of them require your input. In one, for instance, you see something shiny and have to decide whether to get it or leave it alone. If you get it, it could be something valuable, like a diamond, or a piece of glass, which will take away some of your JP. I was told, by a friend, to be careful of a certain random encounter in which your Magikarp can be taken away by a Pidgey.
As with most free games, you can spend real world money to buy in-game items or currency. Perhaps this would help reduce the amount of time you have to wait for your training sessions to refill. I’ve only just begun, but so far I don’t see a real need to spend any real money on the game. It does seem kind of cool, so I recommend checking it out, if you like Pokemon.
A news source: https://www.gamespot.com/articles/a-new-pokemon-game-is-out-now-for-mobile/1100-6450325/