var graphClient = CreateGraphClient(...);

// Then, get the desired drive to work in.
var drive = await graphClient.Me.Drive.GetAsync();

// To get folder from a known folder Id:
var knownFolderId = "someId";
var driveItem = await graphClient.Drives[drives.Id].Items[knownFolderId].GetAsync();

// Or, to get user's root folder in OneDrive:
var driveItem = await graphClient.Drives[drive.Id].Root.GetAsync();

// Pass starting item to a new OneDrive folder
var oneDrive = new OneDriveFolder(graphClient, driveItem);

// Interact with OneDrive via the storage abstraction.
// Extension methods GetFilesAsync and GetFolderAsync also available.
await foreach (var item in oneDrive.GetItemsAsync(StorableType.All))
{
    if (item is IFile file)
    {
        using var stream = await file.OpenStreamAsync();
        // ...
    }

    if (item is IFolder folder)
    {
        var root = await folder.GetRootAsync();
        // ... 
    }
}