These abbreviations are a scholarly way of saying, "You get the point."
The term etc. means "and the rest," "and so on." It is usually placed at the end of a short list of things to save the writer (and reader) the trouble of going on needlessly.
When a list of people, rather than things, is involved, use et al. in place of etc.: Joe Smith, Ray Jones, et al., led the team to victory.
Both etc. and et al. require periods, even midsentence.