my 2003 merc sable wouldnt start a friend tried to cross on selonoid now the lights that use to come on when i start my car dont

i have a good friend who is mechanically inclined.i picked him up asked if he wanted to go buy fuses he said no. he said it was wired right(the new starter)so he popped the hood and there is a power distribution fuse box and switched a couple of fuses and car started right up.we made sure the fuse we borrowed didnt go to anything car needed to go and then drove straight to auto parts bought a new fuse and all is good