Complex sentence: During the gap in time, Kakashi hone the Mangekyo Sharingan that he gained from result of Rin's death to master the Kamui ability that allows him to send any targeted object to another dimension.
Split into simpler sentences: During the gap in time, Kakashi developed a Mangekyo Sharingan as a result of Rin's death. With his Mangekyo he is able to send any targeted object to another dimension.