When you create a broadcast you will find it listed on the broadcast page. This table shows the status of each broadcast with progress and success statistics:
In the scenario above, I am broadcasting to the Workplace group 'General'. It shows me the scheduled time of the post and the time it started to process the post.
Users: The number of users to whom the platform will try to send the message.
N.B. For large broadcasts you will often see the orange SEARCHING status, this shows that the platform is still gathering the list of users to whom it will send the broadcast and can take some time to complete. The platform has to check for the various criteria you have set and to whom it applies before the final user count can be confirmed.
Complete: The number of users the platform has so far attempted to send the broadcast, with percentage complete of the total users found.
Success: The number of users to whom the platform has successfully sent your full broadcast, with percentage of those currently complete.
N.B. This does not mean the number of people who have read or acted on your broadcast, just that the message was sent. There are a number of reasons that this may not show 100% - these will all be due to the Facebook API rejecting the post for some reason, e.g. not being able to send to that person because they've blocked the bot.