subfigcaption

\documentclass{article}
\usepackage{graphicx}
\usepackage{subcaption}
\captionsetup[subfigure]{justification=justified,singlelinecheck=false}
\begin{document}
\begin{figure}
\begin{subfigure}{0.45\linewidth}
  \centering
  \includegraphics[width=\linewidth]{example-image-a}
  \caption{}
  \label{subA}
\end{subfigure}\hfill
\begin{subfigure}{0.45\linewidth}
  \centering
  \includegraphics[width=\linewidth]{example-image-b}
  \caption{}
  \label{subB}
\end{subfigure}
\caption{Main fig}
\label{main}
\end{figure}
\end{document}