How do you use "last but not least"?

its a nice way to mention or present the last person or thing in a group, lots of times people. just because they were mentioned or presented last does not mean that they should not be taken as serious as the before mentioned or presented person or thing.
ex. in a say, beauty pageant the last "beauty" to be presented might start with the saying "last but not least" so and so...
or the last car in a car auction would get the same... "last but not least" the ford whatever.

It means the last of the list of things you are mentioning, but simply because it is the last mentioned doesn't mean it is any less important than the ones you mentioned before it. In other words, you aren't listing things in order of their importance and you are making note of that.

When you're naming something last place, or last on the list, which is not least in value.
Ex. First we have Anna, Second is Bob, and Last, but not least, John.

Basically, when you are giving a list of things, when you come to the last one, you can say "and last but not least" before you list it. Its means that although you have come to the last item on the lists, being last does not make it the least important.

For example
Today for dinner I had:
Meatloaf
Mashed potatoes
Gravy
and last but not least, a salad.

Just like 'PS', and in speech can imply the end and draw back attention.