Action manage pages typically show many different numbers, all representing different things. Therefore, don't be alarmed if they're all slightly different.
In the upper right of action manage pages there is typically a goal slider or count of the number of actions taken. This is typically sometimes a de-duplicated count, so if someone takes action more than once, they will only be counted once here, not twice, and sometimes not, depending on the action.
Down below you will see tabs below the main section which give you access to different information and features to manage that action.
One of the tabs is labeled "Statistics" and clicking on it will bring up useful graphs and charts about your action's performance.
The graph at the top of the statistics tab usually counts de-duplicated action takers per day, so you can see how well your action is doing over time.
The charts below keep track of raw numbers without de-duplication (so you'll see two counted if someone takes action with the same email address twice) and show both the number of activists who took action as well as the number brand new to your email list, so you can track list growth.
The websites chart tracks which websites activists came from before they took action. So if you've posted a link on Facebook, you'd see facebook.com in the list along with numbers showing how many activists and new activists took action. If you've embedded a widget on another website, this chart will also show that website as activists take action using the widget.
The referrer chart tracks referrer codes. So if John Smith posted a link to your action with his referrer code on Twitter, you could see exactly how many activists and new activists John Smith brought it. This gives you a measure of accountability -- if your ally has promised to send an email linking to your action, as long as they're using a link with their referrer code attached, you'll be able to see exactly how successful that email was based on the activists it brought in.
The sources chart tracks the number of activists and new activists who took action from links with source codes, as explained here. The source code "widget" will be added for activists who took action using a widget.