Adding to what Steve said…
First and foremost, you can’t record series if you’re not paying for the Guide subscription.
You can record a series starting from the Live TV 14-day guide, but that’s not common. To do that, click on the show and look around the screen. On Android, you’re taken immediately to the show screen, so you can record the series or individual episodes. On Roku, you get a choice of “Record episode” or “Go to show,” and if you go to the show you can record the series. On the web app, there are “INFO” and “REC” buttons, where the REC button records the episode and the INFO button takes you to the show screen where you can set up to record the series.
Generally, though, most people will set up a series recording by using one of the Guide categories (Prime Time, TV, Movies, Sports, or whatever your particular Tablo app gives you). You may need to select an option in that Guide category to display the shows. Then click on the show, and you can easily record the series from there.
As Steve noted, when you record a series, you are given the choice of recording all episodes which includes reruns, or only new episodes. A caution: the Tablo has to rely on the Guide data as to whether the show is “new” or not. Occasionally, especially on shows that previously aired in other countries (Canada, UK, etc.), the guide’s idea of “new” may be different from your idea of “new,” so check the upcoming episodes to see if they look like the ones you want recorded will be recorded. (An example: if you set up to record new “Death in Paradise” episodes on PBS, you probably won’t get any episodes recorded).