This wikiHow teaches you how to adjust the opacity of layers in Adobe Photoshop so that you can see or hide images in the layer(s) below.
Steps

Step 1. Open the image you want to edit
Do this by clicking CTRL + O (Windows) or ⌘ + O (Mac), select the image file you want to open, and then To open clicking in the lower-right corner of the dialog box.

Step #2. Click Window
This is in the menu bar at the top of the screen.

Step #3. Click on Layers
The "Layers" menu window appears in the lower-right corner of the Photoshop window.

Step 4. Click on Layers
This is a tab in the top left corner of the "Layers" menu pane.

Step 5. Click on a layer
Each layer is displayed with a thumbnail in the lower part of the "Layers" menu window.

Step 6. Click on ?
This is to the right of the percentage next to Coverage at the top of the "Layers" menu and a slider will appear.
If the opacity options are grayed out and you can't click them, you may need to unlock the selected layer first. When a layer is locked, there is a padlock icon to the right of the layer name. Click the padlock icon to unlock the layer

Step 7. Click and hold the scroll arrow

Step 8. Drag the arrow to set the opacity of the layer
Drag the scroll arrow to the left to make the layer more transparent (lower percentage) or to the right to make it more opaque (higher percentage).
If a padlock icon appears in a layer, it is locked or partially locked. In that case, double-click the layer and set the opacity percentage in the dialog box that appears
Tips
- If you don't want to try out the opacity yourself by scrolling, you can manually type a number in the box that contains the opacity percentage as this also changes the opacity.
- Photoshop changes the opacity as you scroll, meaning you can see the opacity change as you change the sliding scale.