According to Rashi, the second aliyah actually happens after the giving of the Torah. Here, Yisro finds Moshe sitting before thousands of people from morning to evening and acting as a judge in their disputes. He would tell them what the laws of G-d say about their particular case.
Yisro suggests a system of delegating Moshe's responsibility, where Moshe would appoint heads of thousands, heads of hundreds, heads of fifties, heads of tens, able men, G-d fearing men, men whose word will be believed, for them to judge most cases leaving only the most difficult for Moshe.
