To make it simple, after creating an account, the exchange will allow you to buy an amount of a cryptocurrency in exchange for your euros/dollars (they usually take a fee for that). Be careful, in reality, you don’t really “own” the cryptocurrency you will buy there: if you don’t own the private key, you have a “promise” that an exchange owes you some assets.
Most exchanges also offer tools for trading cryptocurrency. For example, Coinbase provides this tool.
More interesting in our case, most exchanges offer API for trading like the coinbase API. Thanks to this, instead of spending hours trading in front of your computer, you can write a program that trades for you. That’s the goal of our bot.
One last point, some exchanges offer a sandbox that allows you to trade on the “simulated platform” with fake assets. For example Kucoin.