Remember in gumshoe there are two types of skills investigative and general.
Investigative you get the clue automatically if you have the skill; if you want to spend a point, you can get above and beyond. You do not roll for these.
General Abilities you will roll a d6 to use it, you must always spend at least 1 point to use. You can spend more than 1 to increase your odds of success.
From the rules:
Quote:
1. Spend any number of points from the
relevant General Ability.
2. Roll an ordinary six-sided die.
3. Add the number of points spent to the
number rolled on the die.
4. If the total is higher than or equal to a
Difficulty Number set by the GM, you
succeed. If it’s lower than the Difficulty,
you fail, and something bad happens to you.
So when you roll:
In the reason, put what skill you are using (note how many points you are spending). Then in the roll, put 1d6+whatever you spend.
so you will always have at least a +1.