To recover a deleted deal, go to the list view. Then, from the filters (on the right hand side), select 'all deleted deals':
This will give you a list of all the deals that are visible to you and deleted. From there, find the deal you'd like to restore, clicking on it in the list, then clicking 'restore' in the top right of the detail view. Your deal will then be restored to the stage and pipeline from which it was deleted.
If you'd like to restore more than one deleted deal, select the deals you would like restored from the deleted deals filter, then from the bulk edit menu that will appear on the right select Status > Replace Existing Value With > Open.
If you have a lot of deleted deals, this list can also be further filtered. Simply select 'create new filter' from the dropdown, then in the 'Show deals that match ALL of these conditions' section add Deal > Status > Is > Deleted from the dropdown menus, then add any other parameters you'd like to filter by, name your filter and click 'save'.