Dig down in the earth to create a place for your foundation. This should be a done by a professional crew of workers and planned by a licensed architect or builder.
Lay the ICF down first. The different pieces will lock together, somewhat like building blocks, forming the underlying structure of your foundation.
Add steel reinforcement in selected locations. Steel rebar should be placed in several specialized locations to reinforce the structure and form a further nexus for the concrete pour.
Pour concrete into the ICFs. Fill in the rest of the foundation with concrete also.
Leave the ICFs in place. They should dry with the concrete and become an insulated portion of the structure that will protect inside and out.