Once you created the offers into Interaction schema (nms:offers) you have to configure the offer engine to make it choose the rights offers for your recipients. For this you have to configure some eligibility rules for these offers. Theses rules can be based on your data model (recipients info). You can also add some ranking rules to display the offers in a proper order.
When all set it up then you go to your workflow and chosse "let the offer engine chosse for me". You just tell the engine how many offer proposition you want per recipient.
Afterwards you just need to display the offer renditions for proposition1, 2, 3, etc. .. as you decided in your delivery HTML using JS personalization tags