You can get pretty close by zooming in on the map, then right-click on the nearest spot, and select Create User Waypoint.

If you want to edit the lat/lon value, you will need to convert to decimal -- divide the minutes part by 60. So 59 degrees 09.0 is 59 + (9.0 / 60) = 59.15

and 5 degrees 12.3 minutes is 5 + (12.3/60) = 5.0383333

If you have degrees minutes and seconds, like your second example, divide the seconds by 60 to get the decimal minutes, and then divide minutes by 60

so 58 27 37 = 58 27.61667 = 58.460278

You can also edit the lat & lon after you've created the waypoints, from the Manage User Waypoints dialog, on the Data menu.