'phile' [ means love, so an electrophile which loves electrons and a nucleophile is something which
loves nuclei. So, the nuclephilic pi-bond attacks the slightly positively charged hydrogen in H-Br. The what was an alkene
then has positive charge on one of the carbon atoms which forms the point at which the Br nucleophile can then attach and bond to.
But why does the Br attach to the terminal carbon atom - have a read and see if you can find an explanation.