As two actions, you briefly stop the flow of time. You can take one additional turn in what appears to others to be no time at all. No time passes for objects that you aren’t wearing or carrying or other creatures, both of which are invulnerable to your attacks, and you can’t target or affect them with anything.
Once you take the extra turn, time begins to flow again for the rest of the world. If you created an effect with a duration, such as cloudkill, it starts to affect others, but it doesn’t have any of the effects that happen only when you first cast the spell.
Splintered or partitioned minds within your own mind, such as might be in effect through the use of spells such as schism, act in the normal flow of time.
You can increase the number of turns by 1 for each additional mana expended.