Does an account user know when someone access their account?

That depends entirely on whether the system administrator has enabled the features of the OS that cause it to display past logins to the user. If they enable the feature, then it may show the user the most recent attempted and successful logins, from which the user can identify if someone else has been accessing their account. As an example: If you see that the last login was 12 hours ago and you haven't logged in for 2 days, you know something is up.