IN
1. to indicate inclusion within space, a place, or limits):
Example. I was walking in the park.
2.indicate inclusion within something abstract or immaterial
Example. I work in politics.
3. indicate inclusion within or occurrence during a period or limit of time
Example. I will be done in ten minutes
ON
1. supported by or suspended from:
Put your package down on the table; Hang your coat on the hook
2. so as to be attached to
Hang the picture on the wall. Paste the label on the package.
3.so as to be a covering or wrapping for:
Put the blanket on the baby. Put aluminum foil on the food.
4. The television set was on.
Both very frequently used as prepositions, adverbs,adjectives