Mork von Ork is almost right. If there is a monster in your space and you perform any other action but attacking (like exploring or moving), you must make an evade check. To do this, you test your dexterity modified by the value at the top right of the monster token. If you fail the monster damages you. Regardless of whether you pass or fail, you may then search the room (unless the attack killed you of course).
When the monster is not in your space you can explore the room without having to perform a test.
Hope this helps.
Ohhhh, "space", that's what I missed, I was thinking entire room.