How did the Emperor Constantine the Great impact christianity?

Despite my comment above, I'm happy to give you a few points that will help you on your way:

Constantine's reign was significant to Christianity in (at least) 3 main ways:

1. He was (arguably) the first Christian Emperor.
2. He "legalised" Christianity - His edict of toleration (edict of Milan) gave Christians the freedom to worship without persecution.
3. He convened the (first) council of Nicaea - Bishops and associated clergy came from across the known world to examine and make decisions in council on some important theological issues.

As a result of the Battle of the Milvian Bridge on October 28,312, the Chi Rho become a very popular Christian symbol.

The Chi Rho is one of the earliest cruciform symbols used by Christians. It is formed by superimposing the first two letters of the word "Christ" in Greek, chi = ch and rho = r. Although not technically a cross, the Chi Rho invokes the crucifixion of Jesus as well as symbolizing his status as the Christ. The earliest evidence of the Chi Rho symbol is Constantine's use of it on the labarum, the imperial standard, in the early 4th century CE. Lactantius, a 4th century Christian apologist, reports that on the eve of the Battle of the Milvian Bridge in 312 CE, Constantine had a vision of God in which he was commanded to mark his men's shields with the Chi Rho symbol. After Constantine's success at the Milvian bridge, the Chi Rho became the official imperial insignia. Archaeologists have uncovered evidence demonstrating that the Chi Rho was emblazoned on the helmet and shield of Constantine as well as those of all of his soldiers. Coins and medallions minted during Constantine's reign also bore the Chi Rho. By the year 350 CE, the Chi Rho began to be used on Christian sarcophagi and frescoes. [A.E.M.]

Also see this Wikipedia link on the Labarum

As a result of the Edict of Milan in 313, the Church was able to live in a relative freedom against persecution, Christianity became a legal religion.

Constantine passed numerous laws, encompassing such mundane matters as making the occupations of butcher and baker hereditary. More crucially, supported converting the coloni (tenant farmers) into serfs—laying the foundation for European society during the Middle Ages.

Constantine's laws, in many ways, improved upon those of his predecessors, and enforced and reflected his Christian reforms though they also reflected the growing violence of his age, as the following examples suggest:

•For the first time, young females could not be abducted (this may actually refer to elopements, which were considered kidnapping because girls could not legally consent to the elopement).

•A punishment of death was mandated to anyone collecting taxes over the authorized amount.

•A prisoner was no longer to be kept in total darkness, but must be given access to the outdoors and daylight.

•A condemned man was allowed to die in the arena, but he could not be branded on his "heavenly beautified" face, just on his feet (because God made man in his image).

•Slave "nurses" or chaperons caught allowing the girls they were responsible for to be seduced were to have molten lead poured down their throats.

•Gladiatorial games were ordered to be eliminated in 325 C.E., although this had little real effect.

•A slave master's rights were limited, but a slave could still be beaten to death.

•Crucifixion was abolished for reasons of Christian piety, but was replaced with hanging, to show that there was still Roman law and justice.

•Easter could be publicly celebrated.

•Sunday was declared a day of rest, on which market activity was banned and public offices were closed (except for the purpose of freeing slaves). However, there were no restrictions on farming work (which was the work of the great majority of the population).

The Council of Nicaea:

More significantly, in 325, Constantine summoned the Council of Nicaea, effectively the first Ecumenical Council. He called it because of the social discord and disunity caused by arguments between Christians of different beliefs. Christians within the empire, and thus the empire itself, were divided over what they believed about Jesus and the Trinity. In Alexandria there was a group who were followers of Arius with whom the majority of Christians disagreed. The resulting argument led to threats to close the port and thus had economic and political implications. Constantine wanted to end this disagreement and called the council on the advice of Bishop Hosius of Cordoba.