I have only added diced fruit to my beer, not pureed fruit.
The amount varies depending on the fruit and the beer. In general, about one US pound per one US gallon is a good starting point for most fruits. What do you have in mind?
I added a 49 ounce can of Raspberry puree to a 5 gallon secondary. I gently mixed it in. A few days later I gently stirred it in again, so the yeast could get to all the stuff that was on the bottom.
There were glugs here and there for a couple of weeks.
Afterwards I got a strong Raspberry flavor and aroma.