"El rana" would be for a nickname.

Example:

El rana robó un banco.

El rana robbed a bank.

"La rana" would be for metaphors or comparisons.

Example:

Mi marido Diego es como las ranas. Le encanta el agua.

My husband diego is like a frog. He loves water.

Hot chocolate= Chocolate caliente.

colloquially we say... let's have "chocolate con churros".

Churros is the popular sweet you mention. At least in Spain.

I hope I have helped you.