I'm writing the sentence "This TV show shows examples of behavior that can harm--" and then I list a bunch of things. Should it be a solid dash or two dashes like I wrote? Thank you.
No dash or hyphen. What you need in that place is a colon (:).
http://grammar.ccc.commnet.edu/grammar/marks/colon.htm
In this case, you should use an em dash (—) to indicate a pause or interruption in the sentence. Depending on the formatting you are using, you can create an em dash by typing two consecutive hyphens (--) and the software will automatically convert them into an em dash. However, if the software you are using doesn't automatically convert the hyphens, you can manually insert an em dash by using the following keyboard shortcuts:
On Windows: Press and hold the Alt key, then type 0151 on the numeric keypad.
On Mac: Press and hold the Option key, then press the hyphen (-) key.
Alternatively, you can copy and paste an em dash (—) from a character map or special character tool.
So, in your sentence, it would be: "This TV show shows examples of behavior that can harm—"
Remember, the em dash should not have any spaces on either side—this creates a distinction between an em dash and an en dash.