How to enumerate 1; 2.1; 2.2; 3?
\documentclass{article}
\renewcommand{\labelenumii}{\theenumii}
\renewcommand{\theenumii}{\theenumi.\arabic{enumii}.}
\setlength{\leftmarginii}{1.8ex}
\begin{document}
\begin{enumerate}
\item Initials
\item Age
\stepcounter{enumi}
\begin{enumerate}
\item Preliminary Condition
\item Support
\end{enumerate}
\item Imaging
\end{enumerate}
\end{document}
If you are willing to sacrifice automation entirely, then you could use custom labels throughout:
\documentclass{article}
\begin{document}
\begin{enumerate}
\item [1] Initials
\item [2] Age
\item [3.1] Preliminary Condition
\item [3.2] Support
\item [4] Imaging
\end{enumerate}
\end{document}
Here is an automated version using enumitem
:
\documentclass{article}
\usepackage{enumitem}
\setenumerate[1]{align=left,label=\arabic*}
\setenumerate[2]{before=\stepcounter{enumi},label*=.\arabic*,leftmargin=1.2em,align=left}
\begin{document}
\begin{enumerate}
\item Initials
\item Age
\begin{enumerate}
\item Preliminary Condition
\item Support
\end{enumerate}
\item Imaging
\end{enumerate}
\end{document}