I just accidentally discovered there is a Bash builtin help (by typing hel for auto-complete), and it is really helpful.

The following is an example:
$ help help
help: help [-dms] [pattern ...]
    Display information about builtin commands.
    
    Displays brief summaries of builtin commands.  If PATTERN is
    specified, gives detailed help on all commands matching PATTERN,
    otherwise the list of help topics is printed.
    
    Options:
      -d        output short description for each topic
      -m        display usage in pseudo-manpage format
      -s        output only a short usage synopsis for each topic matching
        PATTERN
    
    Arguments:
      PATTERN   Pattern specifiying a help topic
    
    Exit Status:
    Returns success unless PATTERN is not found or an invalid option is given.
You can read the options, arguments, and explanations. I realized I had spent (wasted) too much time on scrolling and searching in Bash manpage for the same stuff.