Brush tool in Lightroom doesn't work (trial version)

Hello, I'm using a trial version of Lightroom and I'm trying to adjust parts of my photo with the brush tool but it doesn't seem right. More specifically, when I try to increase the exposure, instead of the brushed part getting brighter, it just get whiter, like I'm literally painting white color on top. Is this how it's supposed to be or do I have to pay for the full version to unlock this feature?