There are three things in the rules that I’m aware of that talk about fighting with two weapons:

1. There is a subsection in the basic rules called Two-Weapon Fighting. These are the base rules for anyone using two weapons (BA attack without ability modifier, must use light weapons)
2. There is also a fighting style called Two-Weapon Fighting available to fighters and a couple of specific subclasses (Swashbuckler has that option, I think). This fighting style allows you to add your ability modifier to the off-hand attack.
3. There is a feat called Dual Wielding (Player’s Handbook) that grants additional bonuses: the weapons don’t have to be light, a +1 AC bonus, and you’re able to draw or stow both weapons at once.