When you begin staking, you begin at a 1X bonus multiplier on your reward earnings. This multiplier increases throughout the trial period, to a maximum of 3X after two months. An easy way to think about it is: each additional month you hold, you receive 'an extra X' on your multiplier, up to a maximum of 3X. For example, holding for an entire month gives you a 2X multiplier, and holding for two months, a 3X multiplier.