General uses:
* Ar: This is the most common translation, used for things that are located on a surface. For example: "The book is on the table" would be "Mae'r llyfr ar y bwrdd."
* Ym: This is used for things that are located inside something. For example, "She's on the bus" would be "Mae hi ym y bws."
Specific uses:
* I: Used for movement towards a surface. For example, "He jumped on the bed" would be "Neidiodd i'r gwely."
* Yn: Used for being in a specific state. For example, "He's on fire" would be "Mae e'n llosgi."
* Ar ôl: Used for something happening after something else. For example, "On Monday" would be "Ar ôl Dydd Llun."
Other translations:
* Am: Can be used for "on" in the sense of "about" or "concerning." For example, "The article is on climate change" would be "Mae'r erthygl am newid hinsawdd."
It's important to consider the context to choose the most appropriate translation.