# Resizing the text in the section

I am trying to develop some lecture notes. My code is as follows:

\documentclass[12pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage{titling}
\newcommand{\subtitle}[1]{%
\posttitle{%
\par\end{center}
\begin{center}\Large#1\end{center}
}%
}

\newcommand{\subsubtitle}[1]{%
\preauthor{%
\begin{center}
\large #1 \vskip0.5em
\begin{tabular}[t]{c}
}%
}

\title{Symplectic Geometry in Classical Mechanics }
\subtitle{Lecture 1}
\subsubtitle{Basics of Manifolds}
\author{}
\date{\vspace{-2.0cm}}

\begin{document}

\maketitle
\section{Why Symplectic Geometry?}

It is a mathematical formalism underlying
\begin{itemize}
\item Geometrical Optics
\item Classical Mechanics
\item General Relativity
\item Quantum Mechanics
\end{itemize}

Such a unifying formalism help us to solve problems in one area of physics
by using ideas from another areas.
It doesn't work for systems with loss, friction or noise.

\end{document}


The size of the text "Why Symplectic Geometry?" is too big? Can I reduce its size? Also there is too much white space between the border of the page and the starting point of text on either side. Is there a way to increase the width of the each and every line.

For the first question, you can use titlesec in its simplified \titleformat* command.

As to the margins, you can choose their values with package geometry. Here is a possibility, to be adapted to your needs. I took the liberty to simplify the code for the \subtitle command:

\documentclass[12pt, a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[hmargin =2.5cm, showframe]{geometry}
\usepackage{titling}
\newcommand{\subtitle}[1]{%
\posttitle{%
\par\vskip\topsep
\Large#1\end{center}
}%
}

\newcommand{\subsubtitle}[1]{%
\preauthor{%
\begin{center}
\large #1 \vskip0.5em
\begin{tabular}[t]{c}
}%
}

\title{Symplectic Geometry in Classical Mechanics }
\subtitle{Lecture 1}
\subsubtitle{Basics of Manifolds}
\author{}
\date{\vspace{-2.0cm}}

\usepackage{titlesec}
\titleformat*{\section}{\large\bfseries}

\begin{document}

\maketitle

\section{Why Symplectic Geometry?}

It is a mathematical formalism underlying
\begin{itemize}
\item Geometrical Optics
\item Classical Mechanics
\item General Relativity
\item Quantum Mechanics
\end{itemize}

Such a unifying formalism help us to solve problems in one area of physics
by using ideas from another areas.
It doesn't work for systems with loss, friction or noise.

\end{document}