to start with it would be a good idea to understand first what the blockchain is and how it works, try to understand how the technology works because that way you will be able to follow developments of bitcoin. For example you might have heard about "forks" or Bitcoin version, the only way to understand these is if you understand how the technology works. Once you understand the blockchain, the second step is to understand Bitcoin (Bitcoin is the first application of the blockchain) once you've understood blockchain and bitcoin you'll want to find a way to buy it. The way to buy bitcoin is send fiat currency (indonesian rupiah) to an exchange and they will send you bitcoin in return. The problem in your case is that there might not be any regional exchanges (who support the indonesian market), in which case you should search for an international exchange who supports Indonesia (different exchanges support different countries, try to find an exchange that supports Indonesia) when you've found it, you will be able once you registred and provided some documentation, to send Rupiah via a bank transfer or credit card and receive BTC is return. Hope that helped somehow, welcome to the crypto family.