I created reversed cards, but they're not showing up!
In order to prevent it from being too easy for you to answer cards that are based off the same note, Anki automatically buries cards of the same note that are due on the current day when you answer the first card. When you have just created a new deck with reverse cards, this may cause it to appear that there are no reversed cards in your deck at all (since the forward ones will come up first and cause the reverse ones to be buried).
To confirm that this is the case, you can look at the cards in the browser: there should be two cards for each note, and if you click the Preview button and scroll through some of the cards, they should appear in both directions.
The reversed cards will begin coming up for review on the following day. Alternatively, you can click the Unbury button on the deck overview screen (after selecting the deck from the deck list) and increase the number of new cards for the day from the custom study button. If you prefer, you can also disable this behavior on the New Cards tab of the deck's options.
For more information about how the feature works, please see http://ankisrs.net/docs/manual.html#siblings-and-burying.
Modified note type
Anki's default "Basic (and reversed card)" will generate two cards by default, but you may have modified the note type in the past or imported a modified version from a shared deck that only creates a single card. In that case, you can add a new note type with the default settings by going to Tools>Manage Note Types in the main Anki screen, then choosing "Add" and adding a new "Basic (and reversed card)" note type. If you have existing information that you'd like to use the newly added note type, you can select the existing cards in the Browse screen, then use Edit>Change Note Type to change them to the newly added type that generates two cards.