The timeline records the activities around your Technical file. 

If you have an open invite, you can view the activity here. You can send comments to your supplier if you like. But only if the invite has been accepted.

Tasks

You can also assign a task for your colleague if you work together in ProductIP. Click the Add Task button.
The follow up is the person you assign the task to.

Notes

You can add notes to your timeline for certein activities. You can set them as active or done. When active, it will be shown under open activities.
When done, your note will be shown in the history.