1)
Why did they offer Olos and Shelamim? h
1.
Ramban (Bereishis 19:8): The Olos were to atone for improper intent, that they relied on their strength. The Shelamim were Todos; they viewed themselves as a remnant saved from Binyamin's sword. All such people should offer Todos (Tehilim 107:22, 27:6).
2)
How could they offer Korbanos? The Mishkan was established in Shilo, and Bamos were forbidden!
1.
Refer to 2:5:1:1-3 and the note there.
2.
Radak: Here, "Beis Kel" refers to Shilo.