How to number the sections consecutively

The solution is to use counterwithout as shown here. However, since the April 2018 release the functionality of the chngcntr package has been integrated directly into the LaTeX kernel, so you can just use

documentclass{scrbook}

% usepackage{chngcntr} % not necessary in recent distributions
counterwithout{section}{chapter}

begin{document}
tableofcontents

chapter{First}
section{Foo}
section{Bar}

chapter{Second}
section{Baz}
section{Bla}

end{document}