spacing
For this minimal example
\documentclass{article}
\begin{document}
\noindent
Hallo \\
How \\
Are \\
\vspace{15cm}You?
\end{document}
There is no vertical space created between the word Are and You. How can I add vertical space between them? Using \vspace* did not work either.
In this elementary instance, you can use the following:
\documentclass{article}%
% The [demo] option is just for this example
\usepackage[demo]{graphicx}% http://ctan.org/pkg/graphicx
\newcommand{\HRule}{\rule{\linewidth}{1mm}}
\setlength{\parindent}{0pt}% Just for this example
\begin{document}
\centering
\includegraphics[width = 5.0cm]{logo.png}\par
\kern\dimexpr-\baselineskip-\parskip+2mm\relax
\HRule
\end{document}
Here \kern inserts vertical space. Since the \Hrule is set on the baseline and in a new paragraph, the vertical distance is reduced by \baselineskip+\parskip. An additional 2mm pushes \Hrule down far enough to leave a 1mm gap between the image and the line.
So, for example, if you want a 10bp gap between the image and your \Hrule, you would use
\kern\dimexpr-\baselineskip-\parskip+1mm+10bp\relax
In general, if you contain your images inside a figure environment, you can modify the length \intextsep. For this, read the layouts documentation.
How about this? Note that an \newenvironment has three mandatory arguments: the name, the pre-code, and the post-code. Also the line-ending % signs are often required to prevent stray spaces from being introduced (they are not needed for this example, but I place them there as a best practice).
EDITED in response to Barbara's comment and using cgnieder's suggestion. I verified that extra space is no longer added by having the environment start at the top of a page. Thanks to them both.
Further EDIT. David correctly points out that playing with \leftskip is dangerous. I tried to allay his concerns by defining it as a change, not in absolute terms, but that, apparently is not sufficient. Thinking I will leave it to the experts, I will delete my answer... which I can only do once the OP unaccepts it.
\documentclass{book}
\usepackage[nopar]{lipsum}
\newenvironment{myenv}{%
\par%
\addtolength{\leftskip}{4em}%
\vspace{2em}%
}{%
\par%
\addtolength{\leftskip}{-4em}%
\vspace{2em}%
}
\begin{document}
\lipsum[1-2]
\begin{myenv}
\lipsum[3-5]
\end{myenv}
\lipsum[6]
\end{document}
Best Answer
\vspaceif used mid paragraph, as here, stores the vertical space in a special place (a vadjust node) which is then inserted after the paragraph has been broken into lines, after the line on which the space is added. in your example the\vspaceis added in the last line of the paragraph so the space comes after the paragraph. Compareto add a space at the linebreak you should use
but it is almost always wrong to use
\\at all apart from its use in tables.