Function read 

pub fn read(
    key: impl Into<String>,
) -> impl Future<Output = Result<Option<Vec<u8>>, StorageError>> + 'static

Reads the value stored under key. Ok(None) when there is none, which is what the first run of an application finds.

The operation is placed when this is called, not when the future is first polled, so operations on one key apply in the order they were called even if nobody awaits them.