For a bit about the language, read `3bcw` as move `b`ackward by `3` words and `c`hange the `w`ord under the cursor.

The general form of `b` is `[count]b` where

    [count] An optional number that may precede the command to multiply
            or iterate the command.  If no number is given, a count of one    
            is used, unless otherwise noted.  Note that in this manual the
            [count] is not mentioned in the description of the command,
            but only in the explanation.  This was done to make the
            commands easier to look up.  If the 'showcmd' option is on,
            the (partially) entered count is shown at the bottom of the
            window.  You can use <Del> to erase the last digit (|N<Del>|).

    b       [count] words backward.  |exclusive| motion.

https://vimdoc.sourceforge.net/htmldoc/motion.html#b

For `c` it’s

    ["x]c{motion} Delete {motion} text [into register x] and start
                  insert.  When  'cpoptions' includes the 'E' flag and
                  there is no text to delete (e.g., with "cTx" when the
                  cursor is just after an 'x'), an error occurs and
                  insert mode does not start (this is Vi compatible).
                  When  'cpoptions' does not include the 'E' flag, the
                  "c" command always starts insert mode, even if there
                  is no text to delete.

    {motion} A command that moves the cursor.  These are explained in
             |motion.txt|.  Examples:
                 w           to start of next word
                 b           to begin of current word
                 4j          four lines down
                 /The<CR>    to next occurrence of "The"

https://vimdoc.sourceforge.net/htmldoc/intro.html#{motion}