\documentclass{article}
\usepackage[showframe]{geometry}%<-------------only for check, remove in finals
\usepackage{lipsum}
\usepackage{tabularx}
\begin{document}\noindent
\begin{tabularx}{\textwidth}{lcX}
Category & Data & Explanation \\
AA & 1.2 & \lipsum[1][1-3]
\end{tabularx}
\end{document}