Open your factory, select a recipe, activate the factory, connect up the hoppers, and you have automated crafting.

• At idle, it tries to craft an item every 20 ticks (1s).
• If it can craft an item, it switches to crafting mode, and craft an item every 8 ticks (0.4s), same speed as hoppers.
• If it can't craft an item, but you have enough items, it will split one of the stacks, and move it to an empty slot. (so 1 split per 20 ticks = 1s)

Video review: