When can a new ledger instance be created?

In which scenarios Daml creates a ledger instance implicitly.How can I create a ledger instance. Can Daml Script and other tools create new ledger instances?

First of all, wecome to the community @Ishan_Jaiswal!

Daml abstracts from the ledger implementation so, you cannot spawn new instances of a ledger using the Daml language, neither implicitly nor explicitly. Your Daml application connects to a Ledger API (even if through a JSON API) which is provided by either a Sandbox or Daml Driver which is connected to the appropriate storage tech.
You can spin up a new sandbox ledger using the daml assistant: Daml Sandbox — Daml SDK 1.17.1 documentation
When you are running your script inside daml studio or via daml test, each script run is executed against its own ledger.