In this technique, you will be blending two wet colors and met them in the center to blend. Usually it's more applicable when two different values you want blend just like from darker blue to light blue. Make sure that paints are wet while doing this to make the blending smooth.
This technique usually applicable when there's a dry layer of underpainting. And all you have to do is to add a second wet layer to create a good blend. This is mostly used in acrylic painting due to the fact that acrylic dries fast.
This blending technique will require a glazing medium for acrylic, you can use water but I don't recommend it because you're gonna need to put lots of water to blend it and water will make the acrylic binder unstable and it can have a problem for the preservation of your painting. In this technique you just have to use one color only and add glazing medium to make it fluid. Just spread the wet paints until it become so thin, the thin part will serve as the lighter value.