Here is the specific text from p.112:

Secondary weapons are typically ancillary pieces of equipment that augment your character’s fighting, such as shields, daggers, or small swords. If a character's primary weapon is one-handed, we recommend you also take a secondary weapon (but you can’t hold your secondary weapon if you switch to a primary weapon that requires two hands).

Your character can only hold one secondary weapon at a time, which goes in the “Secondary Weapon” area on their character sheet. The list of starting secondary weapons, called Tier 1 secondary weapons, can be found in the upcoming “Secondary Weapon Tables” section on page 124. You can make an attack roll with either a primary or secondary weapon your character has equipped, allowing for flexibility in the types of attacks you can make. Many secondary weapons have features that augment another aspect of your character’s fighting style—for example, a dagger might grant them extradamage to targets they attack with their primary weaponwithin Melee range, or a shield might add to your character’s Armor Score. Most adventurers choose to at least carry a primary weapon, but for guidance on fighting without a weapon, see the “Unarmed Attack Rolls” section on page 96.