Location contexts other than the one currently being defined have a small fixed-radius bluish base.
Use a long-click on the map to select a location for this context.
Use the pull-down selector under the map to specify the radius for this context.
Important: if your radius is too small compared to the accuracy of the fixes you are receiving, your context may never go active. If you can't get a fix, try increasing the radius. Typically, a good radius would be around twice the accuracy of the fixes you are receiving.
Tap on the map to bring up zoom controls and buttons to enable the Satellite Overlap (left) and Street View (right). Note that the Street View sometimes does not update until the map is dragged slightly.
If you have no internet available in order to retrieve the map tiles, you can still use the Get Fix button (see below) to specify your current location.
Acquires a location fix using the enabled and available providers (make sure the GPS Button is clicked first if you want to use GPS).
Once a fix is acquired, the latitude, longitude and radius of this location context are set according to it. If you reduce the radius after a fix, Tasker may no longer accurately detect whether you are in or out of the context.
When trying to determine current location, Tasker will keep going with fixes until they stop improving (e.g. as the GPS locks on to more satellites). If you get impatient you can press the Get Fix button again to stop the process (its label is changed to Stop while a fix is being acquired).