The possible issue when - without enough experience/knowledge - a new user fiddles with firewall rules is that he can (accidentally) leave some big holes in it, hence the suggestion to start from a solid base instead from nothing.
This should help:
and should it also make you understand why rules are processed in the order they appear on each chain separately. (the grouping is only advised for readability, it doesn’t change anything in how the rules are applied).
A full example is here: