Explain the entire process of a volcanic eruption

A volcano is an opening in Earth's surface. Magma and gas rise through the opening and burst forth. Well, the type of the eruption depends mainly upon the properties of the magma (viscosity, composition, volatile content, etc). Eruption of basaltic magma is less viscous and hence effusive which is mostly lava flow and less violent. On the other hand the ryholitic magma which is more viscous (as well as high volatile content) leads to explosive eruption where gas cloud and pyroclastic materials are expelled. 

Given below is a general idea about the stages in which a volcano erupts.
The process starts with the upward buoyant movement of magma from the asthenosphere through the lithosphere. The magma resides in a chamber at shallow depth.This reservoir periodically empties to the surface through a pipelike conduit in repeated cycles of central eruptions. Lava can also
erupt from vertical cracks (fissures) and other vents on the flanks of a volcano in a pattern known as fissure eruptions.
(Courtesy: Understanding Earth, 5th edition page no. 272)

Pumice, Pyroclastic flow, Landslide, Lava etc are not the stages of volacanic eruption. Instead they are the different terms associated with the products of a volcanic eruption. Pumice is a volcanic stone with lot of cavities. Pyroclastic flows are high-density mixtures of hot, dry rock fragments and hot gases that move away from the vent that erupted them at high speeds. Landslides take place when the flank of the volcanic crater rapidly flows under the effect of gravity. Lava is the magma that comes to the surface after eruption.

It is useful for historians to write narratives so that history can be passed on from their point of view.  think about a story being told in third person, then think about it again being told in first person, by someone who actually experienced the event.