The key is in your own words 'simple and easy' Keep it simple and easy.
I would recommend that you 1st explain what SFI is and what TripleClicks is. You cannot explain one without referring to the other.
The aim here is to be brief and simple.
Tell the people that you talk to that SFI is the 'mother company' that owns an online store called TripleClicks.
Explain that our role is primarily to be sales people and promoters of the store. If the people we refer to the store buy from the store we get commission on their purchases and on any other purchases thereafter as long as we remain members of SFI. There are other income streams in SFI but the store is the main one.
Our other role is to be promoters and recruiters of SFI. The people that we recruit we sponsor and coach into the business and help them become successful promoters of TripleClicks and recruiters for SFI themselves.
Make sure that you know the facts about SFI/TripleClicks so that you can answer questions they may have. A good source is the article 'SFI by the numbers' in the SFI News.