The How-to guides in the Offchain workers category illustrate common use cases for offchain operations.
It is important to note that offchain storage is separate from on-chain storage. You can't send data collected or processed by an offchain worker directly to on-chain storage. To store any data collected or processed by an offchain worker—that is, to modify the state of the chain—you must enable the offchain worker to send transactions that modify the on-chain storage system. For examples of how to prepare an offchain worker to send transactions, see Add offchain workers.