IPC ka Confusion - Bhai kya hua hai?

Maine apni classes mein seekhaya hai ki IPC ke Section 300 mein murder ki definition diya hai. Kaha jaata hai ki jo bhi murder karta hai, use IPC ke Section 302 ke under trial kiya jaata hai. Lekin, maine ek case dekha hai, Nazrudeen vs Emperor (1936), jahaan court ne section 302 ka application karna mana kiya tha. Phir mainne socha ki yahaan koi chhota sa difference ho sakta hai. To mere dost ne bola ki ye difference hain - voluntary vs involuntary, aur jo bhi voluntary murder hota hai, use IPC ke Section 302 ke under trial kiya jaata hai. Lekin maine abhi tak samjhaya hi nahin hai. Koi bhai ya bechare ka jawab do please!