Insertion Sort works like sorting cards in your hand. You pick up a new card and slide it left until it fits.
We pick the second element (2). This is our 'Active' card.
Is 5 bigger than 2? Yes. So 5 must move to the right to make room.
Move 5 to the right. Now we have a 'hole' at index 0.
Hit the start of the array. Drop 2 into the hole.
Next card: 4. The Left side [2, 5] is sorted relative to itself.
5 > 4? Yes. Shift 5 right.
Check next neighbor: 2. Is 2 > 4? No. Stop!
Drop 4 into the spot after 2.
Next: 6. Compare with 5. 5 > 6? No. 6 is already in the right spot! (Best case scenario).
Last card: 1. This will need to slide all the way down.
6 > 1 (Shift). 5 > 1 (Shift). 4 > 1 (Shift). 2 > 1 (Shift).
Drop 1 at index 0.
Notice how fast '6' was handled? If an array is nearly sorted, Insertion Sort is extremely fast (O(n)), beating even QuickSort and MergeSort.
Simple, stable, and amazing for small or partially sorted lists.