Short answers, pulled from the story.
The civil wars of the Tetrarchy began in 306 AD with the usurpation of Maxentius and the defeat of Severus, and ended in 324 AD with the defeat of Licinius by Constantine I at the Battle of Chrysopolis on the 18th of September 324.
The Tetrarchy was a system of shared imperial rule instituted by Diocletian in 293 AD to govern the Roman Empire. It divided authority between four emperors: two senior Augusti and two junior Caesars, with Diocletian and Maximian as the original Augusti and Galerius and Constantius Chlorus as their Caesars.
On the 28th of October 312, Constantine defeated Maxentius near Rome at the Battle of Milvian Bridge. Maxentius drowned in the Tiber after being pushed into the river by his own fleeing soldiers. Constantine's army bore the Chi-Rho symbol on their shields, which Constantine reportedly adopted following a vision before the battle.
The Edict of Milan was an agreement between Constantine and Licinius, reached during their meeting in Milan in 313 AD. It granted full religious tolerance to Christianity and all other religions, legalized Christianity, and ordered the restoration of property seized from Christians during Diocletian's persecution.
Maxentius declared himself Emperor at Rome in 306 AD, capitalizing on his father Maximian's popularity with the army to repel both Severus and Galerius when they marched against him. He was ultimately defeated and killed at the Battle of Milvian Bridge on the 28th of October 312 by Constantine, whose army had swept through northern Italy, taking Verona, Aquileia, and Ravenna before reaching Rome.
Constantine became sole emperor after defeating Licinius at the Battle of Chrysopolis on the 18th of September 324. Licinius surrendered at Nicomedia and was initially exiled to Thessalonica, but in 325 Constantine had him arrested and executed on charges of conspiracy, along with Licinius' appointed Caesar Martius Martinianus.