Consider $\left(1+\sqrt{2}\right)\left(1-\sqrt{2}\right)$. Multiplication can be transformed into difference of squares using the rule: $\left(a-b\right)\left(a+b\right)=a^{2}-b^{2}$.
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $6$ and $5$ is $30$. Multiply $\frac{-6+6\sqrt{2}+\sqrt{6}}{6}$ times $\frac{5}{5}$. Multiply $\frac{\sqrt{5}}{5}$ times $\frac{6}{6}$.