What have you actually got?
Most of what comes out of a sideboard is silver plated. Some of it is solid silver worth many times more. A little of it is steel worth nothing at all. Two minutes settles it, and you do not have to become an expert.
Run a magnet over everything
Silver is not magnetic, and neither is silverplate. Anything a strong magnet grabs firmly is iron or steel, so it is neither, and it is worth nothing to us.
You do not have to pick it out. If it is already in the box, send it. We recycle it for you at no charge and your receipt shows it at no value, so nothing is quietly counted as silver. The only thing not worth doing is paying to ship a box of it on its own.
One exception that catches everybody: a magnet sticking to a knife BLADE is normal on almost every knife ever made, plated or solid. Test the handle, not the blade.
The quickest answer is a photograph
You do not have to learn hallmarks to sell your silver. Photograph the mark with your phone, send it, and a team member tells you honestly what it looks like and roughly what that is worth. No sign-up, and nothing about it commits you to selling.
Plate, or solid silver?
Turn the piece over. The mark is on the back of a handle, the underside of a base, or the rim of a tray.
Now put it on a scale
Plate is bought by the pound, so a weight is all the calculator needs. Sterling is paid at a published rate too, and it is worth many times more.