\documentclass[14pt,%article does not have this option
%demo]{article}%extarticle can have that point size
demo]{scrartcl}%scrartcl can have that point size
\renewcommand{\baselinestretch}{1.05}
%\usepackage{amsmath,amsthm,verbatim,amssymb,amsfonts,amscd, graphicx}
\usepackage{graphicx}% Use graphicx instead of graphics
\usepackage{xlop}
\usepackage[utf8]{inputenc}
\usepackage{tabu,mathtools}% moved earlier in the preamble
%\usepackage{xcolor}
\usepackage[margin=1in]{geometry}
\usepackage{lipsum}
\usepackage{showframe}
%\usepackage{mdframed}%why mdframed if tcb is in use?
\usepackage{wasysym}
%\usepackage{sectsty}
%\chapterfont{\color{blue}}%articles don't have chapters
%\sectionfont{\color{blue}} % sets colour of sections
\addtokomafont{disposition}{\color{blue}}
%\setlength\parindent{0pt}
\KOMAoption{parskip}{half}
\KOMAoption{DIV}{16}
\tabulinesep=_20pt
%\usepackage[svgnames]{xcolor}% the package was loaded earlier, this lead to an option clash
\usepackage[most]{tcolorbox}
\newcounter{exa}
\tcbset{
myexample/.style={
enhanced,
colback=yellow!10!white,
colframe=red!50!black,
fonttitle=\scshape,
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title style={fill=yellow!10!white},
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drop shadow,
highlight math style={reset,colback=LightBlue!50!white,colframe=Navy}
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%\newtcolorbox{texample}{my example}% above it was myexample, not my example!
\newtcolorbox{texample}{myexample}
\newcommand{\keyword}[1]{\textbf{#1}}
\begin{document}
\section*{%\LARGE
Regneoperationer}
%\noindent% the parindent is set to 0pt, why using noindent?
%\Large
En \keyword{regneoperation} er en handling, hvor man enten addere, subtrahere, multiplicere eller dividere. %\newline
%\noindent
Der er \keyword{fire regneoperationer}: %\newline
\begin{itemize}
\item Addition ($+$)
\item Subtraktion ($-$)
\item Multiplikation ($\cdot$)
\item Division ($\div$)
\end{itemize}
\section*{%\LARGE
Multiplikation}
%\noindent \Large
Multiplikation handler om gentagne addition. Vi forklarer dette med en række eksempler:
,%\newline
\begin{texample}
\begin{align*}
2+2+2&=2 \cdot 3 \\
2+2+2+2&=2 \cdot 4 \\
2+2+2+2+2&=2 \cdot 5 \\
2+2+2+2+2+2 &= 2\cdot 6
\end{align*}
\end{texample}
\vspace*{1cm}
\begin{texample}
\begin{align*}
5&=5 \cdot 1 \\
5+5&=5 \cdot 2 \\
5+5+5&=5 \cdot 3 \\
5+5+5+5 &= 5\cdot 4
\end{align*}
\end{texample}
%\newpage
\clearpage
\begin{texample}
\begin{align*}
10&=10 \cdot 1 \\
10+10&=10 \cdot 2 \\
10+10+10&=10 \cdot 3 \\
10+10+10+10 &= 10\cdot 4
\end{align*}
\end{texample}
\vspace*{1cm}
\begin{texample}
En bager bager kager og han har wienerbrød på lager. \par
% \noindent
Han bager 40 Wienerbrød og hvert wienerbrød koster 5kr. \par
Hvad koster 40 wienerbrød? \par
% \noindent
Vi kan enten skrive:
\begin{align*}
\text{40 wienerbrød} &= \text{5kr + 5kr + 5kr + 5kr + 5kr (og blive ved 40 gange)}
\shortintertext{ eller vi kan skrive:}
\text{40 wienerbrød} &=\text{5kr} \cdot 40 =200\mathrm{kr}% be consistent, probably a small skip is better, but i don't know what kr is \\
\end{align*}
\end{texample}
\section*{%\LARGE
Division}
%\noindent
Division handler om gentagen subtraktion. Division er det modsatte af multiplikation.\par
%\noindentVi
kigger på en række eksempler:
\begin{texample}
% \noindent
Hvor mange gange kan vi fjerne 3 fra 15 indtil vi ender med 0.
\begin{alignat*}{2}
&15 - 3 &= 12 \\
&15 - 3 - 3 &= 9 \\
&15 - 3 - 3 - 3 &= 6 \\
&15 - 3 - 3 - 3 - 3 &= 3 \\
&15 - 3 - 3 - 3 - 3 - 3 &= 0
\end{alignat*}
% \begin{figure}% Leave out the figure environment
% \centering
% \begin{minipage}[c]{\textwidth}
\centering
\includegraphics[width=3.0in]{division.jpg}\\
{Caption for image}
\label{fig:division}
% \end{minipage}
% \end{figure}%
\end{texample}
\end{document}
The smart way: Calm down and take a deep breath, read posts and provided links attentively, try to understand and ask if necessary.