Listed below are the stages of Cell. Cell is probably one of the greatest creations that Dr. Gero created, next to Super 17.

General facts about Cell:
1) Cell has the ability to do any technique of anybody that he absorbs. He also steals that persons ki when absorbed.
2) Cell is made from the "cells" of all the greatest fighters in the universe (i.e. Piccolo, Vegeta, Goku...etc...)
3) His ego is REALLY HUGE! He actually creates a "Cell Game" to demostrate his power.

Larva Stage
In this stage, Cell was kept in Dr. Gero's labratory until he fully developed and could fend for himself. The alternate timeline had a different fate for Cell. He is developed into the first stage, but then is killed by Trunks.

First Stage
In all reality, this is the actual first stage of Cell. This is probably the most recongnizable form of Cell since this is his form throughout most of the Cell Saga. This is the direct result after the "Larva Form." During this stage, Cell absorbs many humans to increase his Ki (Cell actually absorbs around 3 cities of humans. Gingertown is where he is first discovered.) Cell had the same powerlevel of Piccolo (after fusing with Kami).

Second Stage
The second stage of Cell was my personal favorite of Cell. He is a lot bigger than his first stage and recieves a big power level increase after absorbing Android 17. Cell then easily disposes of Cell and Android 16.

Third Stage (Perfect Body)
This is Cell's "perfect body" stage. Hence the fact DBZ then starts to call him "Perfect Cell." He obtains this body by absorbing Android 18. Cell wouldn't of had his perfect body if Krillin destroyed Android 18. Cell is really, really powerful and none of the Z-Fighters can beat him except SSJ 2 Gohan. Cell actually creates a "Cell Game" to show everybody how powerful he really is. If nobody can beat him, then he was going to blow up the Earth and kill everybody.