How Do I create an additional apple ID

My husband and I have been sharing one Apple ID account for two iphones for several years - we want to set up a family share so that we can have our own pictures on our phones and still share the icloud storage, purchased apps etc. but not have them on both phones. I can't seem to find instructions on creating an additional id- he already has "our Apple ID on his phone" how do we create a new one for him and replace it on his iphone and not mess up my ID (our original one) ?