Could somebody give me an example(e.g. input->output) of what this block does? Explanation is also appreciated.
From the official documentation (which, if your GNU Radio build is intact, you can also access from the documentation tab of your block properties in GRC):
Convert a stream of packed bytes or shorts to stream of unpacked bytes or shorts.
input: stream of unsigned char; output: stream of unsigned char
This is the inverse of gr::blocks::unpacked_to_packed_XX.
The bits in the bytes or shorts input stream are grouped into chunks of bits_per_chunk bits and each resulting chunk is written right- justified to the output stream of bytes or shorts. All b or 16 bits of the each input bytes or short are processed. The right thing is done if bits_per_chunk is not a power of two.
The combination of gr::blocks::packed_to_unpacked_XX_ followed by gr_chunks_to_symbols_Xf or gr_chunks_to_symbols_Xc handles the general case of mapping from a stream of bytes or shorts into arbitrary float or complex symbols.
so, you get a byte in, consisting of 8 bits, and you produce bytes, each of one with bits_per_chunk bits set according to the input. Example (let bits_per_chunk=1, MSB first):
in 0b11110000
out 0b00000001 0b00000001 0b00000001 0b00000001 0b00000000 0b00000000 0b00000000 0b00000000