The Tron movie saga, including Tron: Legacy and Tron: Ares, is a complex story spanning multiple films.
With a 15-year gap between the original film and Tron: Legacy, and another gap before Tron: Ares, the series can be confusing for new viewers.
To help, we'll summarize the key points of Tron, Tron: Legacy, and Tron: Ares, excluding the events of Disney XD's Tron: Uprising, which was cancelled after one season.
Note that Tron: Uprising is technically canon but was cancelled after a single season.
Author's summary: The Tron saga is a complex story of a computer world.