Firewalls are designed to permit or deny connections to your computer. Your personal firewall will usually protect only the computer on which it is installed.
Windows, MACs and Linux systems have firewalls which should be configured if they are not already enabled. Firewalls are also available on commercial Internet Service Provider (ISP) networks. Firewalls cannot stop all intrusions/compromises, however, in conjunction with complex passwords, antivirus protection, etc., they are an additional layer of protection to provide a layer of defense against compromise.