In case you haven't yet found a solution:
There are problably other ways of entering waypoints but here's one method.
Turn the unit on.
Press Menu button.
Select Save Location.
Then edit the new waypoint then select OK.
To navigate to a waypoint (this ios probably where you'll find your downloaded waypoints) from the menu select Where To.
Scroll down to Find Places
Select Favourites
Select My Favourites
Then select your waypoint.
I've found the 705 manual somewhat lacking in detail and the menu is far from being intuitive. Don't get me wrong I love my 705.