I'm struggling to get to grips with the Triangle Inequalities. The problem is I don't really understand what it means. This is what my lecturer has written in the notes:
$$
|a+b|≤|a|+|b|.
$$
First of all, I don't understand why it's less than or equal to.

If I plug in numbers, for example $a=2$ and $b=5$, I struggle to see how $|2+5|≤|2|+|5|$.

If someone could explain this to me I would be very grateful.