As soon as you have created a Joblet, you will find it in your usual Palette of components and thus you will be able to include it in the place of the transformation steps within your Job.
Like any other component, click the relevant Joblet name in the Palette and drop it to the design workspace to include it in your Job.
Connect the Joblet with the input and/or output components of the Job.
Define all other components properties and context variables, if required, before running the Job like any other Job.
Include other transformation steps following the Joblet if required.
Save and run your Job as usual.