Temporary Aspects placed by a maneuver can be "sticky" or "fragile." A fragile Aspect lasts until it first tagged, then disappears--it's sort of a one-shot, single-use Aspect. Sticky Aspects don't go away the first time they are used; they last until a second action is taken to specifically remove the Aspect.
Example: You can maneuver using Guns to place an "In My Sights" Aspect on a target; this is usually fragile, and goes away when you tag the Aspect for an attack action using Guns versus that target.
Example: A badly misfired
Evocation spell can put the "On Fire!!!" Aspect on the zones that make up a building; this is a sticky Aspect that remains until actions (generally maneuvers) are taken to put out the blaze.
In general, if you want to take advantage of a particular Aspect, you pay a FP and choose one of the three options (see below). If you were the one that placed the Aspect--usually by maneuver, but Consequences taken by your opponent due to your successful attacks also count--you get a "free tag" on that Aspect for a short time (that you may use or pass off, as you said). That tag is free because it doesn't cost a FP to use. If the Aspect is fragile, it goes away after the free tag; if it's sticky, you may pay a FP in later rounds to use it again.
If you want to take any sort of action, and you know of one or more Aspects that should help you succeed, you may pay one FP per Aspect (before or after your roll, as appropriate) and tag each of them for one of the following effects:
- +2 to that roll*,
- a chance to reroll your FATE dice (only do this if you rolled -2 or worse on the dice), or
- invoke the Aspect for effect.
The last option can be the most powerful, but it's also the broadest and sometimes the most confusing option. Invoking for effect is when you note the existence of an Aspect, and then state its relevance to the situation in terms of limiting or expanding options available to someone. This is all about how creative you can be.
Example: You use Stealth to place a "Ninja Ambush!" Aspect on yourself. Next round, you free tag Ninja Ambush! and invoke it for effect as part of a Weapons attack against an unsuspecting enemy sentry. Because this is a Ninja Ambush!, the sentry wasn't expecting your attack, is surprised, and his Athletics is treated as Mediocre (+0) for any dodge against that attack.
Example: In Death Masks, Harry Dresden gets captured and awakens handcuffed under a shower of freezing-cold water. Because flowing water grounds out magical energy, Harry realizes that he can't use magic to escape the situation unless he's able to get out of the water. Essentially, Harry's captor placed the Aspect "Cold Shower" on Harry (and also "These Handcuffs Are Not Fuzzy"), and then invoked it for the effect of preventing Harry from using magic until the Aspect was removed. (These Handcuffs Are Not Fuzzy was also invoked for the effect of preventing Harry from making maneuvers to get out of the water.)
*A small technical detail that most people ignore is that the +2 bonus is what you get if it's obvious or you can quickly explain why this Aspect should help that action. You can pay a FP and tag
any Aspect for a +1 bonus. From what I understand, the +1 option is almost never used, but it's available for when you desperately need that last bit of help and happen to have more FP to burn than relevant Aspects to spend them on, since you can only use any particular Aspect once per action.
