How can I bond with my Hermit Crabs?

I have two girl hermit crab, Carver and Layla are there names, I have had them for about 3 to 4 months but I just don't know how to bond with them. I tried but I never try again, can you help me? Also how do you make sure or know that your hermit crab is happy and healthy. Please answer BOTH questions to get Best Answers Thanks. Samantha .F