From the introduction:
No miniatures or fancy equipment are needed. All you need is the core book, pencil and eraser, two six sided dice, and grid paper, and you can start playing.
You choose four character types from the classic classes (warrior, wizard, rogue, halfling, dwarf, barbarian, cleric, elf ), equip them, and start adventuring in dungeons created by dice rolls and by your choices. 4AD is a nostalgic throwback to the early days of roleplaying, so, while it is NOT a retroclone, it includes a few rules that are homages to that era (treating elves, dwarves and halflings as classes is a nod to that era).
When you enter a room, you generate its content on a series of random tables. You meet monsters, wait for their reaction or fight them, hopefully defeat them (or decide that discretion is the better part of valor!), manage your resources (healing, spells, life points, equipment), grab treasure, dodge traps, find clues, and even accept quests from the monsters you meet. Your characters can level up and become better at what they do… IF THEY SURVIVE.