There are a number of preposition words that change the meaning of a phrase when used with a particular word. For example, you can use Skillful with different prepositions, and you will get a different meaning every time. You can see the examples below:
1. Skillful at
Skillful at (thing)
Example: He is skillful at numbers.
2. Skillful in
Skillful in (doing a thing)
Example: He is skillful in mathematical calculation.