When you get a task you should work on, additional questions or comments might appear. Metatask allows you to communicate on tasks without any additional tools - you can do it right inside the task.
First, access task details page (just click on the task from your task list). On the right side of the page you can find task comments.
To leave a comment, start typing in the comment box at the bottom of the page. Then press "Add"
You can use @mention to ask a question to a particular person (she'll get immediate notification that you mentioned her in task comment)
To attach files to the task, click on the clip button in comments box. You can read more about files in task comments here - How to attach files in task comments
Metatask helps with @mentioning - when you enter @ in comments box, process manager or task assignee is suggested for comment.
Next article - How to attach files in task comments