Pliny the younger is the primary source. Google him and you will find plenty of sites who host complete translations of his work. As for the effect, well, everybody dies? in all seriousness, the eruption blotted out the sun, rained thousands of tonnes of granite and pumice stone down on the city, filled the atmosphere with molten ash and poisonous vapours and buried the city beneath thousands of tonnes of volcanic stone and ash killing everyone and preserving the city almost perfectly for hundreds of years. It also made the area really fertile. The archaeology and sedimentary layers are a source in themselves.