Complex sentence: In the summer of 1999, LaMontagne recorded 10 songs for a demo album that he sent to various local music venues including Maine's Oddfellow Theater, who hired him as the opening act for John Gorka and Jonathan Edwards.
Split into simpler sentences: In the summer of 1999, LaMontagne recorded 10 songs for a demo album that he sent to various local music venues. As a result, the owner of the Oddfellow Theater, in Maine, invited him to be the opening act for John Gorka and Jonathan Edwards.