For an explanation on what kexts are, read this. For a guide to manually installing kexts, check out this post.
OSx86.com (aka Kexts.com) is probably the best outside source for Hackintosh kext files. You need to register an account on the website to download any kexts, which is unfortunate (but then again, requiring registration seems to be common procedure). The website has a very extensive collection of kexts for every sort of Hackintosh issue, and it's a great backup when Multibeast isn't helping you much.
If Kexts.com doesn't seem to have anything to fix your problems, it might be worth asking a question on a Hackintosh forum instead. Just about every Hackintosh forum has an upload feature, and besides, sometimes you need help finding the right kext in the first place. Of course, tonymacx86 is always a good choice for help, but don't forget InsanelyMac or Hackint0sh.org.