You can buy such a box off the shelf, or build one. It's a plug-in sub-panel aka a power distribution box. The better class use breakers. Note that this is only the case because you have a 14-50 outlet. A 10-50 outlet would not be acceptable. By the time you get all the parts together a pre-built unit may be the better deal.
Nothing magical about that, but it makes it impossible to accidentally plug a 240V appliance into a 120V receptacle or a 120V appliance into a 240V receptacle. There is a similar 6-20 receptacle for 20A circuits. Install a 6-15 plug on the appliance. There are a bunch of other general "how to wire things up safely" rules along the way. Any appliance that is rated for 240 volts can also be used on a 220V or 208V outlet. Can you plug a 240V dryer into a 120V outlet? For the dryer, you’ll need to carefully go through each internal circuit and figure out how to make it accept 120V. The heating element is the easiest; simply connect the endpoints to 120V instead of 240V. TWsqsgy.