How to pass data between two custom entities?

Hi,

I've created two custom entities in crm online(Crm5)

My Scenario is:

I'll fill up the first Entity say "A". I've created one JQuery ( If an option set field in entity "A" is set to "Yes", it will load Entity "B").

In Entity "B", some of the fields should automatically retrieve data from Entity "A" on page load.

Also I need to Save Entity "A" before Entity "B" loads.

Please guide me through, as I'm new to CRM.