If your image has large areas of background that contrast with the subject, you could start by using the magic cutout tool to click and delete. Use the ‘tolerance’ slider to expand or reduce the area affected, and the undo arrow under the image (or cmd/ctrl Z) to go back and reapply the action if required.
Even if the magic cutout is successful, you will almost certainly need to refine the edges using the lasso selection tool. Or use the lasso to cut out the image from scratch.
Select the lasso and make sure the ‘remove’ button and ‘light’ feather are selected. Zoom in then start to trace the outline with your mouse pointer or laptop trackpad.
Use smooth strokes, ending in a curve to create a series of joined transparent blocks around your image. Finish by selecting and deleting other unwanted areas of the image.