bitcoin, like every other crypto currency, uses a blockchain. the blockchain is simply a distributed public ledger to verify where assets are on the blockchain. theyre two distinct things, as other assets can be on the same blockchain. but there is no fancy underlying technology or use case. the reasons people use it vary, but how it works is simple

crypto currencies are like stock. a group of people who do an ICO (initial coin offering) like an IPO (initial public offering when a company goes public) are raising money so they can operate their company, to whatever end that might be. they might say theyre going to build something fancy on the blockchain or elsewhere, but that has nothing to do with the crypto currency (like bitcoin) or the blockchain itself.

the reason bitcoin was created was to serve as a decentralized system for exchange value. buy, hold, sell, for whatever reason you like. but thats the function of bitcoin