Every button (call to action) on your site is counted automatically once its page is published — there's nothing to switch on. Counting uses your site's analytics, which 2Labs connects for you.
Each button is counted under a plain name made from the page and the label, such as "Programs - Donate". To see a button's name, open its block in the editor: under the button it reads Tracked in analytics as.
The click counts themselves aren't shown in Reports yet. Ask the 2Labs team for them.
If you change a button's words later, it keeps counting under its original name, so its history stays in one place. To count under the new words instead, click Update analytics name to match. Clicks from then on are counted separately from the earlier ones.