A spaced hyphen in this context is shorthand for a spaced en dash, which is functionally exactly the same thing as an em dash (you just don't want to use both em dashes and spaced en dashes in the same book or what-have-you). They're both used for parenthetical statements. There are also spaced em dashes, which are also the same thing. Which you use depends on the convention; most people probably want to use unspaced em dashes, though, but some organizations (including at least in the United Kingdom) use spaced en dashes.
This is similar to how two hyphens together can represent an em dash. If you want it to look professional, use the actual em dashes or en dashes, though.
En dashes that are not spaced have other purposes (e.g. between a range of numbers or years; you might use a spaced en dash between full dates, however). This is why if you copy a date from some site, paste it in an editor and search for a hyphen you sometimes won't find any results within your pasted text.
There are also figure dashes (used in phone numbers and such) and quotation dashes.
You can find ways to type the real characters. On my Kindle Fire HD8, I just hold on the hyphen until a bunch of dashes pop up for me to select between. On Linux (Xubuntu and others), I enable the compose key, and then press the compose key (whichever key I chose), followed by two hyphens and a period for an en dash, or three hyphens for an em dash. In some word processors they might automatically replace your hyphens with dashes, and/or allow a keyboard shortcut to enter dashes.
If you're using formatted dashes in a publication, you'll probably also want to format your apostrophes, single quotes, double quotes, degrees (°) and elipses (those three dots are one character: …). I honestly don't know of anyone offhand who uses figure dashes, professionally or not (and fonts may not always support them), but technically you're supposed to.
If you want to avoid using dashes in your first specified context altogether, use parentheses (but some people don't like that, especially in a novel).
However, it should be noted that both em dashes and spaced en dashes are sometimes used for things other than parenthetical statements (like when someone does something abruptly, or interrupts, which IMO still has the spirit of a parenthetical statement, even though parentheses can't be used there).
Some people might use them to indicate a pause in dialog (I would encourage using a comma instead if you don't have a good reason to do otherwise; e.g. using the dash to indicate that the speaker may have chosen a different choice of words after the dash than originally intended before the dash).
If you'll do a search and replace on your text that involves the spaced en dash, you might consider using unspaced em dashes instead, since spaced en dashes may be used in date ranges and potentially other things, too, and because you may not have a space on both sides when it ends a sentence (so you would need to do more than one search and replace, or do a regular expression substitution).
