Using segments to narrow down the data you are pulling from Google Analytics is one of the easiest things to do in Grow.
To add a segment, click the blue 'Segments' button. From the list that pulls up, choose a segment to sort on.
The id format for for Segments is kind of weird. It looks like
gaid::-4 , where the ID number comes after the dash. Luckily, Grow will insert this for you, so it is just point and click.
You can find more info about segments on Google's page here. It is pretty simple.
You can also filter in addition to adding a segment.
If you have any questions please email firstname.lastname@example.org or chat in on the site.