Q:

How do I draw these two lines on a X,Y graph?

I don't really know much about drawing graphs on LaTex so I am kind of lost here. One of the lines is y=-3 (a horizontal line at y=-3) and the other is y=x-3.
I have as follows:
\documentclass[]{article}
\usetikzlibrary{intersections}

\usepackage{tikz}
\begin{document}
            \begin{figure}[h]
            \foreach \X in {55}
{\begin{tikzpicture}

\draw[clip] (-4,-4) rectangle (4,4);
\begin{scope}[tdplot_main_coords]
\draw [-latex] (0,0) -- (1,0) node[pos=1.5]{$x$};
\draw [-latex] (0,0) -- (0,1) node[pos=1.5]{$y$};
\path (0,-3) coordinate (X1) (0,-3) coordinate (X2) (3,0) coordinate (X3);
\end{scope}
\foreach \X in {1,2,3}
{\shade[ball color=blue] (X\X) circle (2pt);}
\end{tikzpicture}}  
    \end{figure}    
\end{document}

I have this so far, but the points are completely off of the graph. Like I said, I don't really know what I am doing.

A:

For doing plots it is best to use pgfplots (built on top of tikz):

Code:
\documentclass[border=2pt]{standalone}
\usepackage{pgfplots}
%\usepackage{tikz}% Loaded by pgfplots, so don't need this

\begin{document}
\noindent
\begin{tikzpicture}
\begin{axis}
    \addplot [mark=none, thick, red]  {-3};
    \addplot [mark=none, thick, blue] {x-3};
\end{axis}
\end{tikzpicture} 
\end{document}

