Number and % of users, who added name, last name, profile picture and other info - Number and % of new users who added first name, last name, profile picture and other info
Number and % of users, who browsed X posts— Number and % of new users who viewed at least X posts
Number and % of users, who liked X posts — Number and % of new users who gave at least X likes
Number and % of users, who spent X time in the service — Number and % of new users who spent X time in the service
It is important to choose the right event, which we will consider activation, to learn about the aha moment through analytics or in an interview, and the metric will be conversion to this action. Large social networks may not look at activation, because their new users hardly grow, only old ones wake up