When adding or subtraction, we perform the operations from left to right.

Example
\begin{array}{rcl}
\blue{3x+x} - 2x &=& \blue{4x} - 2x \\
&=& 2x
\end{array}

When multiplying or dividing, we perform the operations from left to right.

Example
\begin{array}{rcl}
\blue{4x : 2x} \cdot 3x &=& \blue{2} \cdot 3x \\
&=& 6x
\end{array}

Multiplying or dividing has precedence over adding and subtracting.

Example
\begin{array}{rcl}
2x+\blue{2\cdot 4 x} &=& 2x+\blue{8x} \\
&=& 10x
\end{array}

Exponentiation has precedence over multiplying and dividing.

Example
\begin{array}{rcl}
x\cdot \blue{2^3} &=& x\cdot \blue{8} \\
&=& 8x
\end{array}

First calculate what is in between brackets.

Example
\begin{array}{rcl}
\blue{(3x+5x)}\cdot 8 &=& \blue{8x}\cdot {8} \\
&=& 64x
\end{array}