The Entire Core Rules can be found on this PDF link below, but here are the different aspects covered in the Core Rules
https://www.warhammer-community.com/wp-content/uploads/2023/06/dLZIlatQJ3qOkGP7.pdf
CORE CONCEPTS (PG 5-9): An introduction to the essential rules, terms, and concepts that underpin every Warhammer 40,000 battle.
THE BATTLE ROUND (PG 10-36) From maneuvering your army to unleashing thunderous firepower and brutal assaults, the action in Warhammer 40,000 unfolds in a series of battle rounds in which each player takes a turn.
DATASHEETS AND UNIT ABILITIES (PG 37-39) Every Warhammer 40,000 unit has a datasheet that reflects the characteristics and abilities it can use in battle.
STRATEGIC RESERVES AND STRATAGEMS (PG 41-43): From well-timed Strategic Reserves to deftly executed strategies, gifted generals use all the tactical advantages at their disposal.
TERRAIN FEATURES (PG 44-52) Warhammer 40,000 battles are fought across all manner of grim and perilous landscapes, often strewn with ruins, wreckage, and other obstacles your forces must navigate while they fight.
MUSTER YOUR ARMY (PG 55-56): Before the battle, Use these steps to organize your warriors and war machines into a formidable fighting force.
MISSIONS (PG 57-60) Before committing your forces to war, you must first establish your strategic goals and the nature of the battlefield to be fought over. This section presents the essential steps for preparing for any Warhammer 40,000 battle.