1.  Go to your profile by clicking view profile

2. Navigate To Gratitude and Endorsements towards the bottom of your profile.
3. Click/Tap the blue plus icon to start writing your Endorsement.  

4. For an Endorsement type in the username of the Member you would like to endorse. Make sure to write it out in full, as it is given on their account, as to avoid any search related issues. Make sure to hit send when done with your message!
Note: You can only give the same Member ONE Endorsement. 

Conclusion:

Note that right when you submit your Endorsement the other member will get an email notifying them that they have received your Endorsement. This message will then sit on both your profile and their profile allowing anyone who views either profile to see the history of Endorsements that was sent and received.