Go to Facebook and request an archive of your data in JSON format. You can either import the downloaded file directly, or extract it first and import the containing folder.
The Facebook archive is disappointing in terms of detail, structure, and technical correctness. There are no IDs, so Timelinize has to use individuals' display names as their ID. (This means if someone changes their name later, they will be timelinized as a separate person.) All their JSON strings are improperly encoded (emoji encoded as UTF-8 instead of UTF-16) so Timelinize does its best to reconstruct true values.