Bitcoins are very hard now to obtain mainly because of its price and how it increased in value over time. In terms of how it's made, well, bitcoins or any online currency are not printed or produced, rather it needs to be "mined." Like in the real world, mining resources have a limit, which means that we will eventually run out of the coins. In this case, miners are people on computers which uses it to calculate complex mathematical problems to generate new coins. However, because of the limited resources, as more and more are mined, the longer it takes to obtain a single coin. Before, a regular CPU can do the job, but now it usually requires supercomputers or a group of them to get the job done.