Minecraft wiki entry for Tick, associated text: Functions with tick or load tag are executed
Each dimension is ticked in order of overworld, the nether, and the end. For each dimension:
The time is sent to the client
The world border is updated
Weather logic
Player sleeping logic
If this dimension is overworld:
The game-time and day-time increase
Scheduled functions are executed
For each loaded chunk:
Chunk info is sent to the client
Chunk tick logic
Phantoms, pillagers, cats, and zombie sieges will try to spawn
Entity changes are sent to the client
Chunks try to unload
Scheduled ticks are processed
Scheduled block ticks
Scheduled fluid ticks
Raid logic
Wandering traders try to spawn
Block events are processed
Entities are processed
Block entities are processed
Player entities are processed
The game will try to autosave if it has been 6000 ticks
Packets from client are processed