Linux typically just uses one firewall and instead has many frontends to its firewall.
The firewall is netfilter, who in turn derives a lot of its rules from iptables. While you could try to use iptables directly, it's got quite a learning curve, and thus a lot of frontends are written for it to make configuring firewalls in Linux far easier: Firestarter and ufw are easier, but like with any user friendly application, they won't allow for advanced firewall usage.
there are there types
Linux is used for all types of computers, from servers to desktops to cellphones to embedded kiosks. For almost any purpose that you could need a computer with an operating system, you can use Linux.
Iptables for Linux is the equivalent of firewalls for Windows. Iptables require elevated privileges to operate and must be executed by user root. That is the main difference from configuring other Linux services.
Iptables for Linux is the equivalent of firewalls for Windows. Iptables require elevated privileges to operate and must be executed by user root. That is the main difference from configuring other Linux services.
Windows, MAC and Linux
Usually software but some hardware firewall devices are produced.
The question is unclear. Assuming you are asking usages of linux, well people use it for personal computing. Most of the companies use linux for servers. A Linux based system is free for anyone to use. A linux system distribution can be used in the same way as windows. Almost any application for windows has an equivalent application available for linux that does the same job. Linux has word processing, picture, sound and video edotors as well as their file format converters. It can be used to play many games, play song, watch videos. Linux is available for almost any personal computer available and almost any other computer in use. Most commercial network routers and firewalls are based on linux.
Yes, Linux can be used on a mainframe.
"Types" of Linux are Called Linux Distributions. Linux by itself is only a kernel, you need more than that for a full system, to get this, distro's were develpoed to include all of this to make a Linux system easier to install. Popular Distro's Are Ubuntu, Debian, Fedora, RHEL, Linux Mint, Arch Linux, OpenSUSE, etc, you can find more at distrowatch
Microsoft Windows Apple Macintosh OSx GNU/Linux Unix
Firewalls
can anyone tell me? What types of computer crime do firewalls protect against