You should introduce a pacifier to your baby once breastfeeding is established.
It's best to wait until your baby is at least 6 weeks old before introducing a pacifier to your baby to allow the baby time to get established at using the breast for feeding.
Using a pacifier too soon may lower or slow down your milk supply as the baby may not suck as much on the breast.
A pacifier also requires a different sucking action than breastfeeding does which can confuse the baby.
However if you're bottle feeding your baby, you can introduce the pacifier at any time when bottle feeding and even soon after the baby is born.
If you're planing to breastfeed your baby, you should wait until the baby is 3 weeks to 4 weeks or 6 weeks old to allow the breastfeeding to become established.
Pacifiers can help prevent SIDS because babies don't sleep as deeply when they have a pacifier, which helps wake the baby up if they're having trouble breathing.
A pacifier also keeps the baby's tongue forward in the mouth, so it can't block the airway.
Pacifiers should be weaned off by 2 to 3 years old although some kids use the pacifier until 4 years old and even 6 years old.
Most children are emotionally ready to stop using their pacifier on their own by 2 to 4 years old.
So, you might want to start planting the seed in your child's mind that the day to say bye-bye pacifier is coming.
My own nephew continued using his pacifier around the house at age 8 and finally gave it up by 9 years old but most kids will stop using pacifiers well before then.