Left margin

\par
\begingroup
\leftskip2.5cm
[ ...the text ... ]
\endgroup
\par

start with


• \begin{center}
  \begin{minpage}{}
  ... the text ...
  \end{minipage}
  \end{center}

  
  another solution is to define your own environment in latex preamble

  \newenvironment{myQuote}[2]%
                 {\begin{list}{}{\leftmargin#1\rightmargin#2}\item{}}%
                 {\end{list}}

  in your text than
• \begin{myQuote}{3cm}{5cm}
• the text ... bla bla bla ... the text
• \end{myQuote}
  or with any other values for left and right margin.

same as above with \begin{myQuote}{0cm}{5cm}
or with any other value for right margin.

It is also possible to set the margins without a list environment. Download

Page margins
Changing the documentwide pagemargins is easy with the chngpage. Do not change the variables textheight, textwidth, .. with the setlength-command. Choose always the packages geometry or chngpage!

Hanging indented paragagraphs

\begingroup
\parindent=-3em
\leftskip=3em
[paragraphs following will have hanging indent]
\endgroup