In ShowSim, all the drag-dropping operations occur between the Effect Browser panel and either the Time Line or Script Editor windows, so you’ll want to work with all three of these windows open.  You actually don’t drag-drop onto the position markers on the simulation screen, so if you are used to Finale this will be different for you.  You can still select the position markers in the simulation area as a means of specifying which positions are to be used when creating new cues, you just don't use them as the target point for drag-drop operations.  You still might want to view the simulation area while scripting though in order to see previews of effects that are selected in the Effect Browser.  Having a second monitor is really the best setup to work with since it allows you to put the three working screens on one monitor and then have the simulation area be on the second monitor, otherwise you can resize the Script Editor to allow a portion of the simulation screen to be visible, then adjust the viewpoint in the simulator so that effect previews can be seen in that region.  With smaller sized monitors being so cheap now, even laptops can be converted to dual-monitor setups using USB to RGB adapter cables without spending much money.

The most common methods of placing effects are these:

First record blank cue markers by hitting the space bar while playing the show in cue drop mode (initiated using the button with the red dot on it in the TimeLine), then add effects to the empty cues after the recording session is complete. 

When drag-dropping an effect onto a cue in the script, there are two modes of operation.  In one mode, the dropped effect will create a new effect which will be placed at whatever the current show time marker is set to.  In the other mode, the dropped effect will be applied to whichever cues are selected in the script and will replace whatever is currently on them.  To use this second mode, open the Options drop-down menu on the Script Editor and make sure “drag-drop = replace” is checked.  I believe it defaults to not being in this mode on a new installation, so you will want to turn this on if using the cue drop recording mode to place empty cue markers.

You can also drag effects from the Effect Browser directly onto the Time Line, which allows you to see exactly what time the effect will be placed at before releasing the mouse button to place the cue.  You can also just double click on the Time Line to place whatever effect is selected in the Effect Browser.  This is useful if you have to create a bunch of cues containing the same effect over and over, rather than having to keep going back and dragging the same effect over again.  You can always adjust the time of the cues by dragging them with the mouse after they have been placed.

The other method of adding cues is using the “+ Cue” button on the Effect Browser or “Add” button on the Script editor.  The “Add” button will add an empty cue, whereas the +Cue button will add a cue containing whatever effect is selected in the Effect Browser.

If you select a group of cues on the Script Editor and click the Copy button, those cues will be placed on the Clipboard.  You can then drag-drop from the clipboard as another source of effects, or you can use the Insert button to copy the entire contents of the Clipboard to another point in the show.  The insertion point will be the active show time indicated by the yellow line on the Time Line.  The Clone button will make an exact copy of whichever effects are selected, so only use that one when you want the copy to appear in the same location as the original.  The Replace button will take the contents of the Clipboard and overwrite the contents of any selected cues in the Script Editor.

For versions of ShowSim that have inventory functionality, the Inventory Browser can also be used as an effect source for drag-dropping and works just like the Effect Browser.

Note that you can hold down the right mouse button while dragging the mouse on the Timeline as a way of scrolling it back and forth, which is easier than using the left and right arrow buttons to scroll it.