First, navigate to the Warranty Issues tab:

Select the Warranty Issue you want to share. Scroll down to the Collaborators section and click Add Collaborators:

To share with a single collaborator, select the drop-down below "Collaborators" and search for their name or email address. Once you have made your selection, click Add Collaborator:

When a collaborator is added, they will receive an email with a link to view this Warranty Issue.

To share with a group of users, select the drop-down below Group and search for the group's name. Once you have made your selection, click Add Group:

When a group is added, all contacts in that group will receive an email with a link to view this Warranty Issue. To manage Groups, see this article.