There are many places to get your parts. If you would like to go in person, Best Buy has parts as well as most electronic retailers, however, the issue is that they are overpriced at these locations, and depending on how advanced you want your computer to run you could be wasting hundreds of dollars. Microcenter is a great place to look if you are looking to build a gaming computer however I would recommend looking online first as you can view a much larger quantity of parts in a shorter amount of time. Amazon typically has reliable parts, however, if you want to build as cheaply as possible look at second-hand websites and platforms like Facebook Marketplace and Craigslist. People looking to get rid of their parts that are perfectly good but just a few years old will put their parts up on these websites for sometimes half the original cost. Computer parts lose their value very quickly in their market because they are constantly improving at a rapid rate and the parts people got a few years ago can already be outdated. Depending on what you want to get out of your computer though, this is the perfect place to look for parts.