How can I make a SharePoint custom list containing items which have lists?

Hello all,

I'm new to SharePoint, & for a POC I need to make a list of "Initiatives".  Each initiative has things like a list of milestones specific to the initiative, a list of "next steps" specific to the initiative etc. 

I was thinking of using a SharePoint Custom List & using a form to allowing editing of list items, this initially seemed ok, but I haven't yet figured out how to allow an initiative item to have these lists of other items.

Any help & direction would be appreciated.

Thanks,

Mitch