Complex sentence: During the festival the members of the band met Marek Piekarczyk, a singer in Sektor A. He decided to join TSA as the band's vocalist, and debuted in the new role after a month, at the Pop Session festival in Sopot.
Split into simpler sentences: During the festival the members of the band meet Marek Piekarczyk, a singer in Sektor A. He decided to join TSA as the band's vocalist. He debuted in the new role after a month, at the Pop Session festival in Sopot.