Add a Vignette in Photoshop (Radial Gradient Method)
A vignette subtly darkens the edges of your image to focus attention on the center. The easiest, non-destructive approach is a Gradient Fill adjustment layer set to Radial and blended with Multiply. You can reposition and scale it at any time for the perfect look.

Step-by-step instructions
Add a Gradient Fill layer
Go to Layer → New Fill Layer → Gradient… → OK.
Click the gradient swatch dropdown and choose the third preset from the list (a suitable dark-to-transparent style).
Configure a radial vignette
Set Style to Radial.
Check Reverse so darkness sits at the edges and the center remains light.
Increase Scale to expand the vignette until the center is clear and edges dark.
Click and drag on the canvas (with the Gradient Fill dialog open) to position the vignette over your subject.
Blend and refine the effect
In the Layers panel, set the Gradient Fill layer’s blending mode to Multiply.
Lower the layer Opacity for a subtler result if needed.
Double-click the Gradient Fill thumbnail anytime to tweak the preset, Scale, or position.