bbsl(Bin, Shift) -> % function accepts binary and number
<< _:Shift, % match Shift number of bits into dummy variable _ and
Rest/bits>> = Bin, % puts rest of the bits into Rest variable from Bin variable
<< Rest/bits, % start creating new binary with bits from Rest at beginning
0:Shift >>. % and Shift number of 0's in the end
надеюсь, что это имело смысл