You can sense tremors in the ground beneath you or around you, allowing you to get an idea of where nearby creatures are. If a creature within range of this ability is touching a solid surface that you are also touching, you can sense them with this ability.
Even if a creature is not within range of this ability, if they are touching a solid surface that you are also touching and they use a Movement action on their turn, you gain a +4 Bonus to your Perception check to Search for them with Tremorsense until the end of your next turn.
Note that it is impossible for a PC to gain Tremorsense as a Precise Sense, but not for some monsters; creatures with Tremorsense as a Precise Sense are so attuned to the vibrations around them that they can tell where and how a creature is moving well enough to fight effectively even when completely unable to see.