I adopted a 15 week old poodle who isn’t leash trained/crate trained. Send help!

I brought home a 15 week old poodle last night and walking on the leash has been extremely difficult. He will not walk at all, and the rescue did let me know he has never been on a leash before. My question is, should I practice leash training indoors until he’s comfortable and then take him outside on the leash? Should I bring him out and hope he starts walking? I’m unsure how to go about this.