In order to share a workflow you own, please proceed as described below:
1) go to the https://vlab.geodab.org/ url in your web browser and login (either with your Google account or with a VLab dedicated account that you need to create the first time)
2) Select the "Workflows" menu on the left, which displays the available workflows that are no more under test
3) For the workflow that you want to run, click on the "Create New Experiment" dropdown box below and select the "Share" option
4) this will open a new window that allows you to insert the email of the user you want to share the workflow with.
Please note that the user you're sharing your workflow with will NOT receive any email by VLab. However, she/he will be able to see and utilize the shared workflow when logged in VLab.