burp suite (paid) or zed application proxy (free).

however, nowadays there are "protections" that mobile apps can use to prevent others from studying their traffic. for better or for worse, attackers also created countermeasures to these protections: frida, etc.

guides / tutorials are plenty on the net. if it's not just for fun, you should probably hire a professional to help you. or get proper (paid) training on using those tools i mentioned.