Graphing Equations in Overleaf

This is a done with pgfplots. Maybe it helps you getting started.

documentclass{article}
usepackage{pgfplots}

begin{document}
    
    begin{tikzpicture}
        
        begin{axis}[] 
            
            addplot[red]{2*x};
            addplot[blue]{x/2};
            
        end{axis}
    
        end{tikzpicture}

end{document}

or just with TIKZ:

documentclass{article}
usepackage{tikz}


begin{document}
    
    begin{tikzpicture}
        draw[->] (-3, 0) -- (3, 0) node[right] {$x$};
        draw[->] (0, -3) -- (0, 3) node[above] {$y$};
        draw[scale=0.5, domain=-3:3, smooth, variable=x, blue] plot ({x}, {2*x});
        draw[scale=0.5, domain=-6:6, smooth, variable=y, red]  plot ({y}, {y/2});
    end{tikzpicture}
    

end{document}