You have nothing to worry about. Your brother, being extremely inexperienced and believing that spells are 'useless,' means that chances are he did not cast a curse on you. To truly have an effect, magick requires more than mindlessly chanting a couple of words you found on a website.
If you think he did manage to cast a curse, just take a bath or shower and visualize the curse/negative energies being washed away from you. It may also help to visualize your body being surrounded by a mirror, which will reflect any negative energies sent your way back to the caster.
Now, to clarify "black" and "white" magick for you...
"In truth, there is no such thing as Black or White magick. Magick is neither good, nor evil; neither black, nor white. Magick is determined based on the intent of the caster; one could easily use white magic to harm someone and use black magic to help someone. For instance, if you cast a spell to get a job then you are ultimately taking that job away from someone else so that the position is available for you. Just as easily, you could cast a spell for someone to lose his or her job, and then someone else would be able to receive the newly opened position. Different approaches, but it has the same ending effect. For every action, there is a positive and negative reaction. Thus, it is pointless to label magick as either Black or White.
However, there are some people who prefer to use these labels to distinguish between spells of a particular nature. Black magick can be used to describe any type of magick that is intended to cause ill will (spreading negativity) or involves death/destruction. White magick, on the other hand, can be used to describe any type of magick that is intended to benefit other people (spreading positivity) or involves life/creation.
The main thing to understand from this is that Magick is neither inherently good, nor evil, as it is affected by the intent of the caster. Furthermore, Black, White, and Gray are simply labels.Lastly, every spell you cast will have both a positive and negative effect, so there is no point fussing over it with labels."
-Excerpt from my Complete Basics Guide