Update for ANSYS Mechanical 2019 R2
The Mechanical interface has changed appearance in version 2019 R2 with the introduction of a tabular toolbar, but it can all be summarized in the following few points that you need to remember:
1) If the action you are looking for is related to a specific section of the tree outline, you can find it by highlighting the section heading in the outline (e.g. Mesh) and then going to the Context tab (located at the top of your screen as shown in the image below) and you should see the action that you are looking for.
2) If that doesn't work, type the action you are looking for in the Quick Launch area in the top right hand corner of the window and it will provide you with different actions that match your search. You can then either directly start the action by clicking on the underlined portion or you can have ANSYS show you where the option is located for future reference by clicking on "Take me there" which will appear when you highlight one of the results.
3) If you need to display or hide the mesh, this option has been moved to the Display tab.