How would I implement this as a \newcommand
\LARGE
\ <Text>
\Large
Document class is a article. Essentially what I am aiming for is to use a command such as \formatlarge{<text>} that would output it as \LARGE.
This would be easier than just typing
\Large
This is a heading
\large
Information relating to the heading
Here are some possibilities with a demonstration of their effects...
\documentclass{article}
\begin{document}
\newcommand\sizeswitch[1]{\LARGE{} #1\Large}
Normal text. \sizeswitch{Bigger text.} Medium text.
\normalsize
Normal text.
\sizeswitch{Bigger text.}
Medium text.
\normalsize
\renewcommand\sizeswitch[1]{\LARGE{} #1\par\Large}
Normal text. \sizeswitch{Bigger text.} Medium text.
\normalsize
Normal text.
\sizeswitch{Bigger text.}
Medium text.
\end{document}
You should not use this kind of manual markup for headings, though. Rather, you should use LaTeX's markup e.g. \section, \subsection etc.
Here, I show how to make the section headings use \Large in the ordinary (rather than bold) weight, and how to create a convenience command for setting some text in the \large size at the start of the section (or anywhere).
\documentclass{article}
\usepackage{kantlipsum}
\makeatletter
\renewcommand\section{\@startsection {section}{1}{\z@}%
{-3.5ex \@plus -1ex \@minus -.2ex}%
{2.3ex \@plus.2ex}%
{\normalfont\Large}}
\makeatother
\newcommand\sectionstarter[1]{%
\large #1\par\normalsize}
\begin{document}
By default, sections are formatted in both \verb|\Large| and bold font.
In this document, however, they are merely \verb|\Large|.
\section{A section}
\kant[1]
\section*{Unnumbered section}
\sectionstarter{This is formatted in a medium size.}
\kant[2]
\end{document}
Note that the point here is not (should not be) to save typing. Rather, it it to ensure consistency, readability and maintainability. If you later decide you want all \sectionstarter{} text in bold or sans or something, you just change the definition in the preamble.
\documentclass{...}and ending with\end{document}.<Text>? What is the purpose of the final\Large?\section{Heading}.{\LARGE text }to restore the previous font size. If you want a syntax similar to\section{text}to make a heading, then some\newcommand\Heading[1]{{\LARGE #1}}or\newcommand\Heading[1]{\bigskip{\LARGE #1}\bigskip}could make a more or less formatted fake heading, but as cfr said, you should not use this kind of naïve manual markup for headings.