Hadrdest thing to understand about Bitcoin ?
For me mining bitcoin and where it came from forming wallet ?
Why we must mining for get bitcoin I still don't know about that.
Mining is done to secure transactions by ensuring the transactions included in the blocks do not spend the same output with another transaction that has confirmed before. The deeper it gets, the harder it is to reversed. However, if the transaction is included in the block after the last checkpoint, it is possible to reverse it by 51% attack as you're able to build a new chain faster than anyone else on he network. It doesn't yield much profit either.
Mining ensures a stable distribution of the coins. If it were to get distributed at the start, people would hold monopoly. It also allows users to make an effort by mining to gain those coins.