For information on creating a signup click here.
Once a signup form is created and opened for responding, members of that hub are able to access the form and submit their response. This is done by accessing Signups on your Dashboard or accessing the specific hub and going to Signups in the Hub Navigation. If there is an "open door" on the right side of the signup it is ready for responses.
Click on the title and select the item(s) or time slot(s) you want. Once you check the box or select a number in the drop down menu, click the Save Response button on the bottom left. This will save your response and it will appear in green under the item/time slot:
Notice the name now under the slot and the change in availability on the right.
As long as the Signup form is open, you are able to edit your response if needed.