To restore an archived project, just go to the main dashboard, click the small arrow next to the title "Projects" and select "Archived Projects".
You will now see a complete list of projects that were archived, and from here you can delete or restore them. To do that click on the project info icon.
The next step would be to click on the ellipses and select "Restore".
To restore a trashed task please click on Active in the top bar of the project, and select Trashed from the menu that appears.
On the next screen you will see a list of all your trashed tasks from that project and you can open and restore them. To do this, just click on the ellipsis and select Restore Task from the menu.