STEP 2
Once your new document is opened press D. This will make black as your background color as white as your foreground color. Now I am going to fill the entire image with black color. In the traditional way you can do it using fill tool. Go to edit>fill or press shift+F5.
In the fill dialogue box, choose black as you color. Press OK.
You can also fill your document with black color within one second. As black is my foreground color so by pressing alt+backspace/opt+delete, Photoshop will automatically fill your image with your foreground color i.e. black.
Your photo should look like this.