Most likely you are not a professional sound engineer, and most likely do not have access to high-end recording equipment. If you have a laptop, you probably have a microphone already, and if you have a desktop, you may have a cheap microphone hanging around somewhere (mine is at the bottom of a box of cables). This should be more than enough equipment to get you started, and I give some tips on creating your own sounds, as well as some places to go online to find more that others have shared.
Most likely you already have some type of audio recording software on your computer. This may suit your needs, or be awful. Depending on the operating system you are running, and how much money you are willing to spend, there are ...