Phonology attempts to analyze how and why sounds change in different environments. With articulatory and acoustic phonetics, you are looking at how sounds are produced and what they sound like. To be able to analyze differences, you'll need a large sample base. The best way to gather the samples necessary to study is recording people speak (either extemporaneously or giving them a short paragraph to read). With current technology it can also be beneficial to take a video and watch how the mouth moves during speech (or even an MRI, which allows you to watch the vocal tract during speech creation). Once you have a recording, you'll use things like oscillogram (like a sound wave) to compare whatever aspect of speech/sound you are studying.