I got this puppy yesterday.I have some questions to ask1. How do I get the dog to poop in the sand box I provided for him.2. Is it true that a mixed breed dog cannot be trained or cannot be trained as effectivelyThanx alot

All dogs are trainable, some breeds pick up things faster and some are more stubborn but all are trainable.
Training your puppy should be pretty easy, just always take him out to that sandbox and tell him your words for going potty, I use "Hurry up". In the house keep your pup next to you leashed to your side. Every 30 minutes or so take your pup outside to the sandbox. If you catch him trying to potty inside, quickly scoop him up with a excited (non threathening tone) and rush him to the sandbox. If any accidents happen inside, or outside the sandbox just scoop up the mess and place in the sandbox.
Congratuations on the new puppy!