...
You can share a tab by clicking on the share icon 
(top right corner of a tab).
In the Share with People display, you can add colleagues to collaborate with and choose the type of permission you want to assign them.
...
Once you have shared a tab with a colleague they will receive a notification. 
...
As an owner of the tab you can choose to give viewer or editor rights:
‘Viewer” - can "read only" a shared tab but not edit the tab ...
...
‘Editor’ - can edit/make changes to a tab which is seen live by both owner and user ...
...
The owner of the tab can also select someone to pass the ownership of the tab to ...
...
Users can check who has 'worked on' or is/has 'seeing/seen' the shared Tab by hovering their mouse over the other user’s avatar for an in-app message to appear ...
...
There is also the option to share your tonnage tab via a link as seen below ...
...