Firewalls
Very basically, a firewall can prevent communication in or out of your computer. It can prevent hackers gaining access, and it can prevent spyware contacting outside computers.
Most firewalls have sets of 'rules', and most will ask you if a particular communication is allowed. Obviously if you have no idea what that communication is, or you simply say yes to everything, your firewall becomes useless. Some, however, are more 'user friendly', and automatically allow most popular pieces of software.
If you have ADSL, many routers have built in hardware firewall. Windows XP offers a software firewall, but it is limited. If you've purchased a 'security bundle' for your antivirus, it should have a firewall included.
Unfortunately, free firewalls are very limited these days. ZoneAlarm still offers a free version, and is certainly better than none at all.
Again, there is a good list here. If your needs go beyond ZoneAlarm, then please do some more reading before choosing your software. There are some reviews here.
Most firewalls have sets of 'rules', and most will ask you if a particular communication is allowed. Obviously if you have no idea what that communication is, or you simply say yes to everything, your firewall becomes useless. Some, however, are more 'user friendly', and automatically allow most popular pieces of software.
If you have ADSL, many routers have built in hardware firewall. Windows XP offers a software firewall, but it is limited. If you've purchased a 'security bundle' for your antivirus, it should have a firewall included.
Unfortunately, free firewalls are very limited these days. ZoneAlarm still offers a free version, and is certainly better than none at all.
Again, there is a good list here. If your needs go beyond ZoneAlarm, then please do some more reading before choosing your software. There are some reviews here.