How do I know what a key is mapped to?

To see what a key is mapped to, use the following commands:

    :map 

    :map! 

You can also check the mappings in a particular mode using one of the “:cmap”, “:nmap”, “:vmap”, “:imap”, “:omap”, etc commands. To find out, where the key has been mapped, prefix the :verbose command:

    :verbose :map