ROOFIT: definition of Pdf with resolution model


I am not sure to understand the way a pdf with a resolution model should be define.
I would like to define a power law pdf which could be convolved with another pdf describing the resolution of my instrument. I looked at the RooDecay class and tried to repeat the example with a power law instead but it does not work. Could you explain a bit more the use of the “declareBasis” function?

Many thanks in advance.