Many of us have Melodyne Essential shipped free with our DAWs, and it's quite a useful tool.
What does it do? changes what you've played into blobs that you can move about, here's a simple example
You record you singing 3 notes, A, B, C, but listening to it the C sounds out of tune, by starting Melodyne, you will be able to get it in tune again, by moving it up or down.
No need for Antares Autotune
Simple.
But you can also (depending on the version - I use the Studio version) (the essentials doesn't do that much fancy stuff)
Move it from side to side, so when it starts can be changed...
Or shorten or lengthen the note
Also..
You can copy and paste the note to make a harmony..or a chord (if it's a instrument part) it's very good at that.
I use it most for tuning Vocals and creating harmonies if your singer doesn't do harmonies very accurately, or you have a limited bunch of stems/takes to work with.
It's one of the tools I just would find it hard to do what I do with out it.
No I don't work for Melodyne.
Hope this helps
Rich