What is the Torah referring to when it says "u'Venei Yisrael Asu ka'asher Tzivah Hashem es Moshe"?
Rashi (from Toras Kohanim) and Targum Yonasan: The Torah is referring to the Mitzvos concerning Sekilah mentioned elsewhere - pushing the culprit down from a high place, stoning him and hanging him 1 (Ramban, Moshav Zekenim and Targum Yonasan 2 - and leaning their hands on him, which was commanded in verse 14).
Ramban (citing Ibn Ezra): It means that, from now on, Yisrael carried out the laws mentioned in the current Pesukim. 3
Ramban #1, Moshav Zekenim #1: It means simply that Yisrael carried out the stoning just as Hashem had commanded Moshe. 4
Ramban,#2, Moshav Zekenim #2 and Seforno: To teach us that they stoned him (not out of hatred, but) in order to fulfill Hashem's command.
Ramban: Not leaving his corpse hanging on the tree after sunset, and burying him (Targum Yonasan).
Targum Yonasan also adds burying him.
See Ramban's objection to this explanation. 12:28 and Bamidbar 1:54.
Ramban: As the Torah often does in connection with commands that Hashem commanded Moshe - See for example Shemos 12:28 and Bamidbar, 1:54.
What do we learn from "Oso"?
Refer to 24:14:151:1 and the note there.