Buddy start digging up as much as you can. Rather than concentrating when to buy and where to buy, you first need to understand the basics; why the price changes, why from around $20000 benchmark in Dec 2017 it came down to $8000.
Just consider Bitcoin as any normal fiat currency, but the anomaly is you can understand the logic behind currency rate change, international trade fair changes, market deviation, natural calamities, govt rules etc are few factors which affect fiat currency. But as Bitcoin is not yet governed by any gov. authorities.
Study all this things first, yet if you want to go ahead here I'm attaching the link by which you can easily move forward with a two step verification process.
Check out here: https://blogs.thebitfort.com/a-beginners-guide-to-buying-bitcoin-5de0f6ee5a64