Semblances are made by Sambrian shaping, to resemble life and to carry out specific tasks.
Semblances re"semble" living things. They vary in shapes and sizes. Some Semblances are dangerous, like the ones in the cloud castles. Semblances are not supposed to be self aware however there are magic items that can cause them to be, such as in the case of Lyrus. Another semblance that also appeared in 'Sky Raiders' was the smiley face Cole sees on the caravan after he gets captured in the Outskirts.