Here are some examples of how it can be used:
* "I think you're onto something with that marketing campaign. It could really resonate with our target audience."
* "She's been working on this project for months, and I think she's finally onto something big."
* "The detective is onto something with this new lead, but he needs to be careful not to scare the witness."
Essentially, it implies that someone has identified a promising path or line of thought, and it's worth exploring further.