Et cetera, usually abbreviated etc., comes from the Latin et, meaning and, and cetera, meaning the rest. So et cetera literally means and the rest.
Etc. is best reserved for times when (a) there is no question of what’s being omitted, or (b) when listing every item in a large group would be unnecessary. In this example, there’s no mystery about what etc. indicates:
All non-human primates—monkeys, gorillas, chimpanzees, etc.—exhibit some form of tool use.
And in this example, the author uses etc. because including a fuller list would be unnecessary:
For 99 cents, users can punch in their current mood (sad, tempted, worried, etc.). [Dallas News]
When the reader can’t know what’s being omitted and it’s not clear that there are more items in the list, etc. may signal laziness or dishonesty. In lazy moments, some writers use etc. when they know of only one or two examples but want to create the impression that there are more. Any engaged reader can see through this trick. Here are a few examples:
Cool “student search” home pages could welcome China’s students with identifiable inspirational figures, like animated cartoons, etc., that are of cultural Chinese importance. [Record Eagle]
Coaches lie all the time, and, as you see with Pete Carroll, Lane Kiffin, etc., can you really blame kids for changing their minds? [Courant]
First, I find out what motivates a particular dog. Some dogs like food, others toys, etc. [CBS News]
In each of these cases, it is not clear what etc. refers to, and we can’t simply assume that there are more examples than those the writer lists.
Because et means and, the phrase and et cetera is redundant.
Etc. vs. et al
Et cetera refers to things. Et al. refers to people.
Treat etc. as you would the phrase and the rest. When it comes at the end of a list, put a comma before it if you use the serial comma and don’t if you don’t use the serial comma. (We won’t get into the serial comma issue here.) When it’s in the middle of the sentence, it doesn’t need to be followed by a comma.
Etc. and for example
With a list introduced by for example or an equivalent phrase, there’s no need to use etc., because for example already implies that there are other examples that could be listed.