You buy shares in GLD ETF which holds physical gold for you. The risk is that SPDR collapses or get their assets stolen.

You can also buy gold futures on the futures/commodity exchange which is a contract that specifies the other party has to deliver gold to you in the future. The risk is that the financial system collapses and the broker/clearing broker cannot uphold the contract anymore.

So it depends on your intention for buying gold, if it's to hedge against inflation or market crashes, buy a gold tracking security will be fine. If it's to be used as a doomsday currency, then I think you're better off hoarding canned tuna, vodka and guns; things that you can either barter with, or use to force other human beings to do your wish.