Once your MLS is active, you will see a similar Network Efficiency graph as below on your Home tab. This will show you the number of Deals Won and Deals Missed since joining First or since Jan 1 of the current year. These number will reset at the beginning of each calendar year.
Your Network Efficiency is calculated by dividing the total number of Deals Won by the total number of deals. For example, in the graph below we would take the total number of Deals Won (9) and divide that by the total number of deal (9 +26) = 26%