Strava is a fitness tracking application that is used by irunnersevents.com to track your runs. 
In order to participate and complete distance challenges, it is a requirement to connect Strava to irunnersevents account.
Here is a step by step guideline on how to connect the accounts.

Step 1 - Open a browser such as Chrome or Safari,

Step 2 - Go to Strava website and log in. 

https://www.strava.com/login

https://irunnersevents.com/

Step 4 - Go to Settings and click Connect with STRAVA button

Step 5- Give access to Strava Data - Click Authorize

irunnersevents will be able to:

•  View data about your public profile (required)
•  View data about your activities
•  View data about your private activities