Need Help with a new dog

He just came to my doorsteps few days back with a collar on his neck , I've waited for its owners and it seems like no one is coming for him .
As a person who never owned a dog before , i am seriously in trouble understanding how to approach this .
But him being so good to me , i decided i should keep him

Am here to know the basic things regarding him , like perhaps his probable age , breed ,kind of things
please do tell me how to feed him properly also.

Sorry if its too much to ask , as i said never had an experience before