In Lily’s 7th year, once James stopped being so arrogant and mean, they started to go out. When they left school, they got a house together, got married and had a baby called Harry, but at that moment in time, Voldemort was growing stronger and stronger, and had found out that he needed to kill Lily’s son if he wanted to survive. Lily and James found out about this and went into hiding by using the fidelius charm so no-one could find them. They made Peter Petigrue secret keeper, and this was their mistake. Petigrue had been secretly working for Voldemort for the last year or so, so he told Voldemort how to find them. On Halloween night, a year after Harry Potter was born, Voldemort went into their house. He killed James first, who had tried to defend against Voldemort to give Lily time to run and hide. Voldemort found them and tried to kill Harry, but Lily placed herself between Harry and Voldemort as a shield…

Voldermort killed her.

He couldn’t kill Harry though and this was because of Lily’s sacrifice. If Lily hadn’t sacrificed herself for Harry, he wouldn’t have survived, and wouldn’t have defeated the greatest evil to walk the earth, so Lily kind of saved the world.