The 'Experiment' is what you create using an existing Application in the workspace to submit a job in an external computational resource.
Select an application from the workspace and you would then be able to create an experiment providing the inputs and computational resource queue properties.
After providing the required inputs and creating the experiment either "Save & Launch" or "Save" to launch later.
An experiment may have one-to-one or one-to-many relationship with computation jobs submitted at remote resources.
Image: Create Experiment Page
Submitting a job from the gateway results in creating a Job Script, generating a Job Name, creating a Working Directory for the job in remote computational resource and submitting a job.
Saving and launching a created experiments will submit a job.
Once the job is submitted the remote resource will response back with a job ID.