Board Thread:Theories and Speculation/@comment-24824859-20150704165201/@comment-945885-20150706213910

Seelentau wrote: What Minato was saying is:
 * 発動型ではなく、形態変化をする消えない常備タイプ. ..
 * They're not an invocation type, but rather an indelible reserve type that uses form manipulation...

To phrase it another way, "They're not the type that can be invoked, but rather a standby type that doesn't disappear which can be manipulated with shape transformation."

In short, the user can't invoke (activate) or make them disappear (deactivate) them. Rather, they appear on standby (always on) and can be controlled and manipulated by the user using shape transformation.

According to the databook, they appear/manifest when the user awakens the power of the Sage of Six Paths, and it's not clear if they can ever reform after that initial awakening; Obito's disappeared after he lost his Six Paths power, and got one back when he stole some of that power back from Madara. Naruto was seen losing most of his, and his last three haven't been seen since he used them to counter Sasuke's attack at the Valley of the End. Though he arguably hasn't used Six Paths Sage Mode again since then, either.