First things first, if you don't already have the Music Memos app, download the latest version from the App Store.
Once you have created some recordings using the app, you may want to share them to GarageBand for further editing.
The first step is to go to your memo library. From the main screen of the app, you can either swipe upward on the screen, or you can tap the icon in the upper middle of the screen.
You should then see a list of your recorded memos. Tap to select one, then tap in a blank area of the selection (somewhere other than the name of the recording, which would let you edit the name).
Upon doing this, you should see a "Details" screen, which includes the Share button you are probably familiar with from throughout iOS (for those who aren't, it's the rightmost of the five buttons near the top).
Finally, just select GarageBand from the list of apps to share to in order to send your memo to GarageBand for iOS.
If you are using a Mac and want to send the memo to GarageBand for OS X, tap "iTunes" on the above menu rather than GarageBand. Then you can utilize iTunes File Sharing using iTunes on your Mac to get the project into GarageBand. More details on importing files via iTunes File Sharing available in the last section of: Copying Documents to or from iOS.
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If you use iCloud Drive, you can also go to the Music Memos folder in iCloud Drive, and drag the .caf files to GarageBand for OS X.