Well, that's what it's supposed to do.
Recently, I noticed that Google Keep wasn't reflecting online what was on my phone, and when I did some digging, I uncovered the cause. This may apply to you for other reasons but if you are experiencing these symptoms:
Google Account (or most other accounts) is not synchronising web with device (e.g. Google Keep, Drive, Mail, etc.)
To fix this, you need to check that your Google Account (or most other accounts) is set to sync.
The path to follow is Settings ==> scroll down to Accounts and tap the account type you want to edit...
Select the Account to configure