\documentclass{article}
% --- load packages ---
\usepackage[margin=1in]{geometry} % change the margins
\usepackage{amsmath} % useful math environments and commands like align
\usepackage[colorlinks,bookmarks,bookmarksnumbered,allcolors=blue]{hyperref} % hyperlinks between references
\usepackage{graphicx}  % include images
\usepackage[caption=false]{subfig} % subfigures.  false option prevents conflicts in caption styling with other packages
\usepackage{booktabs} % better tables
\usepackage[capitalise]{cleveref} % better referencing. uses cref.
\usepackage[section]{placeins} % sometimes useful to prevent figures from floating out of a section
\usepackage{cite} % handles multiple citations in one command better
\usepackage{doi} % allow correct hypderlinking of DOIs
\begin{document}
\title{A Simple Example}
\author{Andrew Ning}
% put in \date{} if you don't want a date to appear, or enter a specific date, otherwise default is today's date.
\maketitle
\section*{Abstract}
This section is not numbered (see the star) as would be appropriate for something like an abstract.
\section{Introduction}
Note that \cref{eq:something} is numbered (and hyperlinked)
\begin{equation}
    c_l(\alpha) = 2 \pi \alpha
 \label{eq:something}
\end{equation}
but this one is not.
\begin{equation*}  % note the star
    \int_{-\infty}^\infty f(x) = \frac{3}{x^2}
\end{equation*}
This is an alternative syntax to have unnumbered equations
\[ \alpha \beta = 5 \gamma\]
You can also have equations inline like $4 \delta^2$.  We can also align equations:
\begin{equation}
\begin{aligned}
\text{minimize} & \quad J(x) \\
\text{with respect to} & \quad x \\
\text{subject to} & \quad c(x) \le 0 \\
\end{aligned}
\end{equation}
Or align, but number each one separately:
\begin{align}
x &= 5\\
y + 2 &= 7\\
z + 4 &= x + 7
\end{align}
\Cref{fig:rosen} is showing how to insert, size, caption, and reference a figure.  Note that I used a capital Cref for the start of sentence, and would use a lower case cref to refer to the figure in a sentence (\cref{fig:rosen}).  Also note that I have used a vector-based image (pdf in this case).  This is strongly preferred to bitmap images (png, jpg) if possible.
\begin{figure}[htbp]
\centering
\includegraphics[width=3.5in]{rosenbrock}  % extension not needed
\caption{This are contour lines from the Rosenbrock function.}
\label{fig:rosen}
\end{figure}
The figure will float around the text as needed to get a well-typeset document.  
\subsection{Hello}
This is a subsection.  It contains an unordered list
\begin{itemize}
    \item something
    \item another thing
    \item i don't know
\end{itemize}
and an ordered list
\begin{enumerate}
    \item first time
    \item second time
    \item third time
\end{enumerate}
These can also be nested.
\subsection{Subfigure Subsection}
In \cref{fig:sub} you can see a subfigure example, I can also refer to part of the figure if I want (\cref{fig:sub1}).
\begin{figure}[htbp]
\centering
 \subfloat[first subcaption]{
   \includegraphics[width=0.45\textwidth]{rosenbrock}
   \label{fig:sub1}
 }
 \qquad
 \subfloat[second subcaption]{
   \includegraphics[width=0.45\textwidth]{rosenbrock}
   \label{fig:sub2}
 }
 \caption{Overall caption, which should be a sentence.}
 \label{fig:sub}
\end{figure}
\section{Conclusion}
You can \textbf{bold} or \emph{emphasize} as needed.  Be sure to use ``quotation marks'' correctly (leading backticks, closing pair of single quotation marks).  As we see in \cref{tab:mytable} something something.
\begin{table}[htb]
\centering
\caption{This is a table caption.  Note that table captions go above tables, whereas figure captions go below figures.}
\label{tab:mytable}
\begin{tabular}{@{}lrr@{}}
\toprule
 & a column & another column \\
\midrule
case 1 & 1.30 & 2.30 \\
case 2 & 4.56 & 6.78 \\
\bottomrule
\end{tabular}
\end{table}
This is a regular-dash, an en--dash, and an em---dash. I'm citing an article \cite{article} and a book \cite{book} in this sentence using the attached BibTeX file.
% This is for the bibliography.  Note that it is using sample.bib 
% you would need to provide your own bibtex file.
\bibliographystyle{unsrt}
\bibliography{sample}
\end{document}