Greedy Heuristic for the Traveling Salesperson Problem
First let's name your points $P_A$, $P_B$, $P$, $P_C$, and $P_D$ (from left to right).

With the first heuristic you start at one point ($P$) and move to the closest point. From that new point, you move to the next closest point, and so on and so forth.

With the second heuristic you again start at one point ($P$) but you move to the point closest to one of the two ends of your current path. It is a simple improvement over the first heuristic.

For your example:


Current path: $P$. Closest point to $P$: $P_B$.
Current path: $P-P_B$. Closest point to $P$ or $P_B$: $P_C$.
Current path: $P_B-P-P_C$. Closest point to $P_B$ or $P_C$: $P_A$.
Current path: $P_A-P_B-P-P_C$. Closest point to $P_A$ or $P_C$: $P_D$.
Current path: $P_A-P_B-P-P_C-P_D$. The only choice left is to connect $P_A$ to $P_D$.