There are countless articles on the web about blending acrylic paint with relation to painting miniatures! Try googling: miniatures, painting, blending.
To fully explain would take many paragraphs and pictures, there is more than one way to skin a cat and the same applies to blending acrylic paint... But as so many excellent guides and sources already exist it's not worth the bother really! And if you can't Goggle it I can't be bother to for you.
Sorry but 'how do you blend?' is a bit like 'how do you draw?' or 'how do you make a television?'.
So in the context of the question 'how do you blend' it's probably best answered 'with paint, a brush and skill'...