I am looking into buying a new monitor, how do I know which one I should buy?

It depends a lot on the use case and how much money you want to spend. First decide on a budget. After that you should decide on what size the monitor should have. Then, within that size and budget range take a look at different features such as resolution, color accuracy, refresh rate and connectivity options. A high resolution is good for work and gaming but also requires a good graphics card. Color accuracy is important if you plan to use the monitor for artistic work, such as editing movies and images. Refresh rate is important if you plan to do gaming, especially online. Connectivity options such as power delivery over USB-C is important if you want to simply connect the monitor with a laptop.