The firewall determines if network traffic should continue on to its destination or be stopped.?

A firewall can block/open particular ports without prejudice.

Yes, a firewall does determine if network traffic should continue through to the destination or be stopped. Therefore keeping unwanted materials out.

Yes, firewalls are in charge of deciding whether a piece of network traffic should be allowed past the firewall to travel onwards to its destination or if it should be stopped. Rules can be set at the firewall to prevent traffic from entering your local network that you do not want to.

A modern firewall can be programmed to block or or pass through (with or without modification) packet traffic based on its source or its destination or both. It can select packets based on an IP address, a range of ip addresses, network or subnet. It can use port numbers to filter or redirect packets to specific ip addresses. Better ones can select packets based on the domain name, or part of it or even block based on the contents of a web page. Of course, it may also block access to a really nice chicken breast recipe because of one Word.

Some firewalls can even filter based on the category association of a host or domain name. For example, you can block web sites that involve drugs and alcohol, or sites associated with sex and nudity.