To open the Selector tool use either of the following:
For searching text in a graph's node labels, for example, switch to the [Nodes] tab.
You can choose from different matching types which let you specify whether your text appears at the beginning, at the end, or somewhere in the label's text, resp. whether the node label should match your text completely.
For searching text in a graph's edge labels, you can switch to the [Edges] tab and configure your criteria in a similar manner.
Using [Find..] vs. [Select Elements] has the following differences to it: with [Find..] a single graph element that matches your search criteria is selected and centered in the editor, whereas [Select Elements] selects all matching graph elements at once.
In both cases, you can use [Find Next] (F3, resp. Command-G on Mac OS) and [Find Previous] (SHIFT-F3, resp. SHIFT-Command-G on Mac OS) from the [Edit] menu to have the next/previous matching graph element selected and centered in the editor.