Suppose you are working in SSMS (SQL Server Management Studio) and while working on it, if you want to get more information on a function, you can invoke BOL by pressing F1. If the cursor is inside a function/system procedure/system variables, the BOL opens with the topic specific from where it is invoked
For example, you have typed system procedure sp_monitor in your query window and you want to learn more about it, make sure the cursor is placed anywhere within the word and press F1. BOL opens with the topic sp_monitor.
You can also highlight any function and press F1, BOL opens with that topic
Consider the following piece of code
select * from sys.objects where create_date>'20000101'
Now highlight sp_monitor and press F1 as shown here
BOL opens with the topic sp_monitor
No highlight GETDATE() and press F1.
BOL opens displaying information about GETDATE().
Similarly highlight sys.objects and press F1. BOL opens with the topic sys.objects.
A simple yet smart way to make use of BOL without using the index option!