My baby is 16 months and is walking at home but when we go outside he cant walk and wants to sit ? any advice

Comfort is important: If he is walking without holding on to,anything at home, he can clearly walk! Some children are shy outside of the home until they get comfortable. Maybe he is looking for comfort by staying close to you. Try taking him to the same place with the same people, and let him get comfortable without suggesting he walk. He may want to join in when he is ready.