Consulting shared activities
If you read the article Creating an activity in my activity library for frequent use, you will see that you can share your activities with your team, as well as insert them directly in your scenario.
In order to do this go to the Studio and open the "Resources" tab.
On the left side of the page you will see the following menu:
Click on "Shared activities". You will see the list with all the activities shared by your team.