The earliest you can give a baby teething biscuits or other hard things such as crackers is 8 months of age.
Always supervise the baby when you do give them crackers or teething biscuits or whenever you feed them any food even when they can feed themselves.
It's not advised to give a newly teething baby teething biscuits right away but wait until at least 8 months of age and then you can give them teething biscuits safely.
When your baby is between 4 to 6 months of age the baby can begin eating soft pureed foods and then as they get older and reach 8 months old or older they can eat other solid foods.
That includes the Gerber Puffs and other solid foods such as cereal, apples etc.
When they are little you should cut the foods up small enough so that they can easily chew it and not get choked on the food.
Always keep an eye on the baby and supervise them while eating foods even when they are feeding themselves.