I think that the answer you are looking for is that Douglass decided that he was going to try (sometime in the year 1835) to run away from his master and become a free man living somewhere in the North. He was tired of being kept as a slave and desperately wanted to be free.
He was, at the time that he made this resolution, about 16 years old. He felt that he was becoming a man. He felt that a man ought not to be enslaed and that, therefore, he sould try to become free. Here is a quote showing that this is what he resolved as 1835 began:
I therefore resolved that 1835 should not pass without witnessing an
attempt, on my part, to secure my liberty.