Spot gives a bonus to all tests on Survival abilities made within 2 spaces (remember that range is counted diagonally). A survival ability is any ability with the Survival keyword, so the starting Survival abilities are Hide, Scavenge, and Spot.
Just to repeat, the starting Survival abilities are Hide, Scavenge, and Spot.
Yes, you read that right. Testing Spot improves the chances of testing Spot, with each Spot giving an Awareness apperception.
Remember, you can only test Spot if there is a benefit to be gained. For example, Amy ended her turn on a location with a fantastic Awareness+4 modifier, but didn't have a Spot card, so she couldn't take advantage of it. However, when she draws up, she gets a Spot card. Bob is only a couple of spaces away, so he moves to her location and decides to try Spot. Before he rolls, she uses her Spot as a reaction and succeeds - yes! Another temporary Awareness apperception for Amy, but more importantly a bonus for Bob! Bob is still allowed to test Spot because Amy's Spot goes away at the beginning of her next turn; his turn will last through her turn, providing the team a benefit. He plays his Spot action card, adding the location's +4 modifier along with Amy's Spot bonus of +5 to the party's base value of 4, for a total modifier of +13. He rolls a 10, and makes his Spot check! Huzzah! He gleefully notes the temporary Awareness apperception.
But he's not done - he still has a Peek and another Spot, so he discards his Peek card to move one space and then he decides to play another Spot action card. He is allowed to do this because it will effectively extend the range of his spot for the rest of the party. His location doesn't provide any bonuses, but he does get a Spot bonus. The ability explicitly states that he doesn't get the bonus twice, even though he's within range of two spots. The active Spots gives him a +5, and his temporary apperception (+1) coupled with the party's base value gives him a +10 total. Good luck, Bob!