Timelines are used to mark events that happened on a line. Events on a timeline are placed in order from oldest to most recent. Older events are on the left and more recent are on the right. You read it like you do a book.
There is NO year zero on a timeline.
Long, long ago a man named Dionysius came up with a plan for timelines. He used Jesus' birth on his timeline because he wasn't sure how old the Earth was. They didn't have calendars or smart phones so his idea made sense to people at the time. He used the birth of Jesus because he was a Christian.
An event happening before the birth of Christ is followed by the letters BC which stands for Before Christ. An event after the birth of Christ is followed with the letters AD which stands for anno domini. This is Latin and means after Christ was born. It DOES NOT stand for after death.
Non-Christians or historians might use different initials on a timeline but they still mean the same thing.
They will use BCE (Before Common Era) in place of BC.
They will use CE (Common Era) instead of AD.
Try to place these years into the correct place on the timeline (on the bottom of your study guide)