So you might be newly registered or you might simply have been logged out from a previous visit, but there’s normally a choice between the login screen and the quick login in either case.
The Login Screen
Since this screen (accessed from the Login option of the main menu) is not only where you’ll normally be taken on completing registration but also the first thing you’ll see in any ‘members only’ forum, we will describe it first:
While the Username and Password fields should be self-explanatory, Minutes to stay logged in simply means the number of minutes the cookie that keeps you logged in will last before expiring and requiring you to login again. So it’s not advisable to enter a long time here if you share a computer and are likely to forget to logout, but you might prefer to check Always stay logged in if no-one else has access to your computer.
The Quick Login
Although many forums also have a quick login box to allow you to login direct from any screen, its position on the page may vary considerably from forum to forum. In the SMF default theme, for example, it’s in the collapsable section at the top, whereas it’s more likely to be at the bottom in themes based on the older YaBB SE forum. If you can’t see it and it hasn’t simply been collapsed, it’s either not enabled at all (in which case you should still be able to access the login screen from the main menu) or you’re already logged in (in which case the main menu should include a Logout rather than Login link!).