There are multiple ways to add your friends on Locket, one is by sharing your individual Locket link.
How to share your Locket invite link:
Open the Friends page by using the "Friends" button on the top of the app.
Look for the section called "Find friends from other apps"
Or scroll down to "Share your Locket link"
Share your link on either Instagram, Snapchat, Messages, or Other Apps
You can also copy and paste your link to share.