An example of promotional pricing is a typical "2 for 1" deal or a "Buy One, Get the Other at 1/2 Price" deal. This can be on any product in any supermarket department.
An example of loss-leader pricing is a significantly reduced price on a staple item such as a bag or jug of milk. The supermarket uses this discount on a much-needed everyday item to lure people into their establishment. They hope the customer will buy other items during their visit - hopefully regular-priced items with higher profit margins.
I purchase loss-leader items if I need them. I won't buy an item I don't usually use just because it's on special (unless I really want to try the product).