The basic process for using wireless in Linux is:
- Ensure a driver for your card is loaded.
- Configure the card at the wireless access level, this means setting the details of the specific wireless access point and encryption type (e.g. WEP, WPA).
- Configure the card to use TCP/IP, assigning an IP address, subnet mask, gateway, DNS servers, etc.
For the driver: These are normally implemented as modules loaded into the kernel. Use tools such as lshw, lspci and lsusb to view installed hardware so you know what type of device you have. Using the correct comand line options these will also show drivers (kernel modules) associated with each piece of hardware - if the driver is loaded. Tools like lsmod, insmod, rmmod and modprobe are used to actually manage kernel modules (list loaded modules, add modules, remove them, etc), and there are also a number of configuration files like those in /etc/modprobe.d/ which are used to configure those modules. Thats the background info you need to know.
Regards actually getting the driver loaded (or confirming whether its already loaded), your best bet here is to find what type of card you have via lshw, lspci or lsusb, then Google it to find out more about its Linux driver. If its not already installed and loaded (hint: knowing the module name will help you check) then you need to find out how to get it and install it. If a supported driver exists for your card, Google should be able to help you find out how to install it.
For the layer two and three configuration steps, either use wicd or this or purehates guide in the HowTo section.