Pioneer SPH-DA77DAB adding extra speakers

[KeVan71]

Hi. I have a Pioneer SPH-DA77DAB head unit fitted in my T6. I want to add an extra set of speakers in the back of the van. When I connect them direct to the head they don't work. I have read that they need a separate amplifier but I don't have any idea what type I need or how it's wired. Can anybody help please.

Thank you