The first thing in a latex doc is a \documentstyle command. Add a line below it:
\usepackage{graphicx}
You now have all the commands defined in the package graphicx available to use. One of those commands let's you include graphics files. In its simplest form it is:
\includegraphics{foo.pdf}
Just type it into the body of the document, replacing foo.pdf with the filename of your graph, and recompile. The filetypes you can use depend on how you are compling your document. See the link in my last for what works with what. If your graph is a pdf file, you'll need to compile with pdflatex. If you're running latex from the command line, just type pdflatex instead of latex. If you're using MikTex, there's a dropdown that will let you choose "Latex --> PDF". If you're using something else, have a poke around.
You can get a fair bit of control over how latex displays the pdfs. I gave an example in my last. That one shows the pdf scaled to fit within a rectangle that is 90% of the width of the text on the page and 200 points high. Try specifying one or the other or both, or leaving out the keepaspectratio.
You will want to put the includegraphics command in a figure environment rather than just in open text:
\begin{figure}
\includegraphics[]{} <- you fill in the brackets
\caption{A graph!}
\end{figure}
Latex will put the figure somewhere sensible. You could also write the first line as
\begin{figure}[h]
which asks latex to try to put the figure here. Instead of h you can use t or b (top or bottom of the page). You can also add an exclamation mark to make latex try really hard to place the figure where you asked.
Does that help?