Navigation is a bit different from navigation in the File Browser window. To expand a node and see its contents, click on its handle (clicking on the handle when it is expanded will collapse it again). When you have identified the table you want to open, highlight it by clicking on it, and then click the Open Table button at the bottom.
To move to a different directory, i.e. to change the root of the tree which is displayed, use one of the buttons above the tree display:
(In fact the above navigation options are not restricted to changing the root to a new directory, they can move to any node in the tree, for instance a level in a Tar archive.)