Simple Way to Format Section Titles

Question

Any package documentation that looks like this:

\titleformat{<command>}[<shape>]{<format>}{<label>}{<sec>}{<before-code>}[<after-code>]

is considerably less helpful for the newbie (like me) than examples. It does not give the newbie reader much of a clue as to what exactly ought to be typed into a real document. Do I type in those angle braces? Curly braces? Square braces? What, precisely, goes inside any or all of these delimiters?

Examples are the way to document.

The titlesec documention does have examples at the end, but they are too few, and do not cover the case I'm interested in.

My question is this: what is a simple, straight-forward way to format section titles? There are several design requirements for my output:

1. The section number should not be indented at all.
2. The entire body of the section text should be indented similarly to what the enumerate package does, except that I would prefer normal prose paragraph indenting instead of newlines. That is, the first lines of paragraphs in the section are indented "twice", while the subsequent lines are only indented "once". Here "once" and "twice" mean relative to the section number.

I'm sure there's a way to do this, but my searching here and elsewhere has failed to uncover it. I'd be grateful for any assistance. Thanks in advance!

Here is a minimal almost-working example using the enumerate package. I could almost do it with this package, except for wanting bold section titles and so forth.

\documentclass[12pt]{article}
\usepackage{enumerate}

\begin{document}

\begin{enumerate}[I.]
\item Section Title

This level has a great spacing from the 1. on the left to the first word ``This''. And then, if I want 
a hierarchy, the heading there, an `A.' in this case,
\begin{enumerate}[A.]
\item Subsection Title

is nicely lined up with the indented text above. However, I would like to change
this indenting to use normal prose paragraph indenting, such as
\end{enumerate}
\end{enumerate}

Normal paragraph prose indenting, where the first line is indented, and the rest of the paragraph is not. 
However, the non-indented text needs to be at the indentation of the ``This'' above, and the first lines need
to be indented one more slot, of the same width.

\end{document}

And here's a minimal working example I typed in in MS Word (naturally, I had to man-handle the indenting to be what I wanted):

Answer 1

I am a bit unsure of how exactly you want these indentations to be, So I've created one where the section title would be at the same indentation-point across. The code is based on the example of a section given in the documentation section 9.1 A full example:

\titleformat{\section}
   {\normalfont\Large\bfseries}{\thesection}{1em}{}

To get the same indentation-point, we need to calculate the width of the section-number, as these vary in width, depending on which number is being printed. (8 is wider than 1 in most fonts, and a 100 is ofcourse wider). This can be done with the command \widthof{content} from the calc-package. Then we set the length for the intendation to two \parindents, which is the length of a normal indent, minus the width of the section number.

But as the \parindent is not the same everywhere, and is zero within the \titleformat-macro, we need to calculate it outside of that. Therefore a new length is created, \anIndent, which captures that length.

To get the indentation you want, I grabbed the answer by Werner posted in Indent an entire paragraph / section?. This works across pages, and is easier to use that a minipage. It would ofcourse be great if there was some solution which worked without setting these macroes manually for every section.

Also, do you really want indentation of the first line? I don't think that is a very common way to do it. Normally, the first paragraph is not indented, only subsequent ones.

EDIT: I've now made a new environment, to make the syntax a bit better. It is based upon the adjustwidth-environment from the changepage-package. The new environment is called indentedSection and takes one argument, the number of indentations. 1 for section 2 for subsection and 3 for subsubsection. I also added support for subsubsection

Output

Code

\documentclass[11pt]{article}
\usepackage{titlesec}
\usepackage{lipsum}
\usepackage{indentfirst}
\usepackage{calc}
\usepackage{changepage}

\newlength{\anIndent}
\setlength{\anIndent}{\parindent}

\titleformat{\section}
  {\normalfont\Large\bfseries}{\thesection}{2\anIndent-\widthof{\thesection}}{}

\titleformat{\subsection}
  {\normalfont\large\bfseries}{\thesubsection}{3\anIndent-\widthof{\thesubsection}}{}

\titleformat{\subsubsection}
  {\normalfont\normalsize\bfseries}{\thesubsubsection}{4\anIndent-\widthof{\thesubsubsection}}{}

\newenvironment{indentedSection}[1]{%
    %Input #1: Level of indentation
    \begin{adjustwidth}{#1\anIndent+\anIndent}{}
        \hspace{\anIndent}% Indent first line
        \ignorespaces% Ignor any space at start of environment
    }{\end{adjustwidth}}

\begin{document}
\section{Baz}
\begin{indentedSection}{1}
    \lipsum[2]
\end{indentedSection}
\subsection{Foo}
\begin{indentedSection}{2}
    \lipsum[2]
\end{indentedSection}
\subsubsection{hello}
\begin{indentedSection}{3}
    \lipsum[2]
\end{indentedSection}
\end{document}

Answer 2

Okay, here is a 27 page document explaining titlesec. (If that link doesn't work, try this one.) I'm reading it myself, now that I found it. It has your abominations, but it explains the abominations. That makes it all okay, right? There's also this website that also has an online LaTeX editor; it includes working examples you can open. I'm working on fixing the first link.

Example (direct quote): <command> is the sectioning command to be redefined, i. e., \part, \chapter, \section, \subsection, \subsubsection, \paragraph or \subparagraph.

Hope this helps! I'll keep looking for other resources.

Other Resources

Oh, and in light of Johannes_B's comment, here is the TikZ manual. Very lengthy, and extremely helpful (I just started learning TikZ/LaTeX and that manual is awesome. As well as the wikibook for LaTeX.) Here and here are two more LaTeX resources that are very handy. Here is documentation for Tabu. Finally, here is a TeX stack exchange question about documentation/resources for ConTeXt.

Note: This was posted before the OP updated his question to make it clear that he wanted a problem to be solved; not documentation.