Converting PSD to JPG is something you'll need to do when sharing designs with people who don't have Photoshop — which is almost everyone. The conversion flattens all layers into a single image and compresses it as JPG. Here's how to do it without paying for Photoshop.
The fastest method is Photopea (photopea.com, free). Open the PSD file in your browser, then go to File → Export As → JPG. You can set the quality level and resize before exporting. Photopea handles complex PSDs with layers, masks, and blending modes — the export will look exactly like the intended final image.
On Mac, Preview opens PSD files natively. Open the file, then File → Export → Format: JPEG. Set the quality slider (80-90 is good for most purposes) and save. Preview renders a flattened view, so the result is the composite image as intended.
GIMP (free, cross-platform) can also handle the conversion. Open the PSD file (layers are preserved), then File → Export As → change the extension to .jpg. GIMP will flatten automatically during JPG export and let you set the compression quality.
For batch conversion of many PSD files, XnConvert (free) processes entire folders. Drop in your PSDs, select JPG as the output format, and convert all at once.
Remember: JPG is lossy and doesn't support transparency. If your PSD has a transparent background, the transparent areas will be filled with white (or whatever background colour your tool uses). Use PNG if you need to preserve transparency.