Full definition of spotting from the rulebook below.
Rules Reference p. 19, "Spotting" subsection:
"Some cards require a player to spot a specific game element
in order to use its ability. To spot an element, a player must
have that element in play. Most cards just require a player to
spot a character of a specific color.
Example: Use the Force (Aw 149) says “Spot a Blue character
to turn a die to any side” You must have an undefeated Blue
character on your team, or the card does nothing.
• A player cannot spot their opponents’ characters or cards,
unless the card explicitly says so.
• If a player is not able to spot the required element, then
the card does nothing."
Refer to page 10 of Rules Reference for definitions of what "in play" and "out-of-play" means.
It's also worth noting that you can play the card even if you are unable to spot the specific element; but in such case the card does nothing.
Page 19 of a Rules reference? I only have the 2 page rules that came in my starter packs. Is there an actual rule book of multiple pages out there somewhere?