MPLAB® X IDE provides two methods to find something in the file that is currently displayed in the editor.
The first method, which requires the least amount of effort, is to highlight an existing piece of text (e.g. a variable name, function name, or any other text in your code). The editor will automatically highlight with gold all matches in the current source file. In addition, a gold bar will appear in the error stripe at the far right to indicate the relative position of all instances that have been found in the file. Clicking on a bar in the error stripe will take you to that instance of the highlighted item.
The second method, which is mostly used when you are searching for something that isn't presently visible to highlight, is to select from the main menu Edit ▸ Find…. This will display a bar at the bottom of the editor which contains a text box where you can type in your search term. All matching terms will be highlighted in orange and a gold bar will appear in the error stripe at the relative position in the file of each instance that was found.