Well, the short answer to the question is, you don't.
Not unless you are willing to be knee deep in black smelly sludge, that is.
What you actually do is trade and invest in things directly or indirectly effected by the price of oil.
{ Yahh, the just about everything in use in the modern world we take for granted, lol, but for our purposes in this section, lets stick to the commodities and markets most closely associated. ]
So, you could for instance, directly invest in oil companies, in the expectation of good returns in a recovery.
Or, more relevant here, you could speculate on futures contracts and the fluctuating price over time.
But, seriously, that requires a lot of knowledge which your average home trader hasn't much chance of acquiring fast.
Or you could trade FX or deal in foreign currency day-by-day as events play out.
But the clear near-certainty is that the price WILL go up, that being paid to take oil away was an exceptional anomaly, and that there will probably not ever be another opportunity as good as this one to make money in your lifetime.
So, take a deep breath, and dive in !