For putting figures side by side, check Two figures side by side.
For flushing the caption left, use the caption package as below. The graphicx package was only used here for the demo figure.
\documentclass{article}
\usepackage{caption}
\usepackage[demo]{graphicx}
\begin{document}
\begin{figure}[h]
\captionsetup{justification=raggedright,
singlelinecheck=false
}
\caption{H Feistel Function }
\includegraphics[scale=0.7]{example-image}
\end{figure}
\end{document}
justification=raggedright flushes your caption left.
- The default behavior is to center-align your caption if it fits in one line.
singlelinecheck=false disables this behavior.
There is also no need for the flushleft environment here.
Please always provide a complete minimal working or non-working example (MWE) beginning with \documentclass and ending with \end{document}. Also, please limit your question to one problem at a time. I have answered the part on how to flush your caption left since there seems to be no question yet about it. If there already is, I would be willing to delete this answer to maintain order in this site.
\begin{flushleft}What you have would have generated an error about an undefined environment – David Carlisle Feb 11 '13 at 23:02flushleft. Finally, maybe I'm missing something but what does the justification of the caption has to do with sending the next figure to the next page? Are you trying to put them side by side? – abdulhaq-e Feb 11 '13 at 23:03