Photoshop Stroke belongs to layer style. You can add stroke outside of an image, text or shape. When you apply stroke over something, it looks like a border or outline. You can also choose different colors for stroke. And you can also adjust the size, position and opacity while applying stroke.
Last month I wrote about how to work with Fill & Opacity in Photoshop. I think you should also have a look to this tutorial. It will be helpful for you.
Look at the two images below side by side. The left one has no outline. But the right one has a border outside of it.
No stroke has been applied on the left image. And the right image has a stroke outside of it. You can also use stroke with texts and shapes. Stroke can highlight something. Sometimes after applying stroke over something, you can minimize the fill. In that time, you will get stroke highlighted and the inside dimmed! Learn more . . .
How to Apply Stroke?
If you wanna apply stroke over an image then open it. Or create a new document and then type something or take any shape on which you wanna apply stroke. Now make sure you're on the right layer I mean your image or text is selected. Also make sure that your Layer window is turned on. Now go to the strong as shown in the image below.
Hit on the fx (Add a layer style) at the end of layer panel and choose Stroke. Now you will get the Layer Style window. Look at the Stroke options below:
Adjust the size and look at the effect of your stroke outside the image or text. This is very important. Sometimes 1 px doesn't make any sense. Though it depends on the situation I prefer 2 or 3 px. Certainly a fat stroke will not make any sense.
Keep Position - Outside, Blend Mode - Normal, Fill Type - Color and Opacity - as your wish. If you minimize the opacity from 100% to 60 or 70%, then your stroke color will be darken somewhat.
And finally choose a brilliant color for the stroke. Hit on the color box and select different colors to test the result. After choosing the color, hit on the OK button.
You can also explore some additional options from Layer Style window. Suppose Drop Shadow, Gradient Overlay, Satin, Bevel and Emboss these are really cool options here. These can turn your normal image into an outstanding one. And these are really awesome for creating superb text!
After applying stroke, also adjust the Fill and Opacity of the layer. These control the transparency of your image. Adjusting the transparency will give you a completely different look.