New to Crypto investing and need some clarification on a few terms.

I’m a long term investor in the stock market and pretty comfortable doing research and investing without paying an advisor, but I’m a complete newbie to Crypto.

I swear I feel like I’m in kindergarten. I’ve always been confident about money but this is like learning a foreign language. If there were advisors on these platforms I’d gladly pay them for the education alone.

Question for folks here with more experience. Say I bought crypto on Uphold. Why would I need to put this purchased currency into a “Vault”? And I’ve read alarming stories of people not having their “keys”. Please can someone ELI5?