How do I know if I have ever registered a bitcoin account? Just wondering how I could check to see if I own any bitcoins.  How can you do this?
There are a few different ways you can store bitcoins, there isn't just one place you can log in to and check your balance, like you may be used to with online banking. So if you don't remember having a specific wallet with coins stored in it, then you'll have to go on a bit of a hunt. 

For example, there are desktop full node wallets (eg bitcoin core), litewallets (eg Bread, or Jaxx), paper wallets (a piece of paper with a keypair on it), hardware wallets (eg Trezor or Ledger), web wallets (eg blockchain.info), and 3rd party wallets/exchanges (eg Gemini, Binance). Each one of these is a different method for storing the cryptographic keypairs that are used to generate a bitcoin address, and interacting with the network. Each one will have different levels of security/ease of use, usually a user will select a method of storage based on their personal needs for security/usability. 

If you don't remember specifically what sort of wallet you may have used, then try searching your computer for bitcoin-related files (eg search terms: wallet, bitcoin, btc, etc), as well as your email inbox. Search anywhere you think may hold a clue, such as old hard drives/backups, your internet browsing history, or your social media accounts. 

Good luck!