when to scold or spank your baby?

my mil fetch caden and me for lunch today. on our way back to the house, caden was soooooo fidgety. he kept on standing up and making fake cries. my mil said she can't remember her children being that mischievous. she said she's very strict even when her kids are still young. she doesn't let her kids undermine her. it's like nowadays, we moms give in easily to our kids. we let them do what they like to do. but my baby is only 9 months old =( if my baby can understand already, that's the time i will scold him or spank him. i definitely won't spoil him!
so? when is the right time to teach our baby the right and wrong things? when should we start scolding or spanking him? it's so hard to be a first time parent especially when someone is constantly looking over your shoulder ='( *sob*