Most likely you’ll be able to use your motherboard’s built in ethernet. First, find the type of ethernet card in your motherboard. This can be found in the manual or on the manufacturer’s website.
Unless you are extremely lucky, you will need a kext to enable your internet. Most ethernet built into motherboards can be used; however, a very small number of wifi cards are supported. If you have a prebuilt system or laptop, most likely you will have to purchase a new wifi adapter.
For a list of compatible hackintosh wifi cards see Hackintosh Wifi
Intel Ethernet kext by Hnak Insanelymac development thread
Atheros kext for AR81(31/32/51/52) by Shailua Insanelymac development thread
Realtek RTL8111/8168 kext by Mieze Insanelymac development thread
Note: these are simply some of the most common ethernet kexts. If your motherboard uses a different chip for ethernet, it does not mean you can’t get it working. You will, however, have to do some research. Check out Hackintosh Zone Downloads and Insanelymac Downloads for kexts. Not all the drivers are listed in the downloads section, so be sure to check the forums as well.
If all else fails, you can still purchase an ethernet PCI card.
Installing the Kext
Once you have downloaded the kext, copy it to (/System/Library/Extensions) or (/Library/Extensions) & Repair Permissions & then Reboot to apply the changes.