documentclass{memoir}

pagestyle{ruled}

usepackage{lipsum} % for mwe
setstocksize{3in}{5in}
settrimmedsize{3in}{5in} {*}
setlrmarginsandblock{0.3in}{0.3in}{*}%%%%
setulmarginsandblock{0.5in}{0.5in}{*}
checkandfixthelayout
fixpdflayout

renewcommandchapternumberline[1]{}
renewcommandpartnumberline[1]{}

% suppress section and chapter numbering
%renewcommand*{thesection}{arabic{section}}
renewcommand*{thesection}{}
renewcommand*{thechapter}{}

% Set chapter name on the left
chapterstyle{section}
begin{document}

chapter{first}

Now is the time for all good persons to come to the aid of the
party. That will require enough text to
newpage
get to a second page.

section{first section}

lipsum{1}

end{document}