yes, a SCALE. theres way too much to dwell into such a general topic. everybody asks this question, trying to find the magic answer. theres no magic code for a guitar solo, its just learning scales and practice, practice, practice. some are easier than others. usually blues based solos are the easiest. that doesnt mean that a "blues" scale cant be used for anything else though, i mean, half of anything youve ever heard is probably derived from the pentatonic scale. all rock, be it metal or adult contemporary, is probably built relatively the same. it takes time to realize the similarities between all of them, so dont expect solos to just pop into your head. get a book, learn the beginners stuff. it sucks, but you have to learn to crawl before you walk.