It's not really complicated as to what you might think. From what I understand, Bitcoin is a crytocurrency or a virtual currency which can be acquired from trading with other users, buying from other users or wherever it's sold, and the most common way is by MINING it. Hence the term, bitcoin mining. Before, bitcoin mining was at breeze because there were a few people who use it. Bitcoin mining is like an algorithm of some sort, where in you computer will be forced to work at it's full power in order to solve complex equations or problems (from what I've understand). And today, there are a lot of miners in bitcoin thus it's becoming really hard to mine coins. You also have to have a custom built computer specifically for bitcoin mining. Bitcoin mining is purely GPU intensive. There are a lot of explanations also in YouTube or other websites.
Also, do not get shocked when you stumble upon an article or a news or a video, showing a whole building dedicated for bitcoin mining. I heard in some part of China I think, there were slaves in a factory where they operate the bitcoin mining thing and it's brutal.