Your washer is splashproof, which means that any accidental spray that comes back to your washer will not cause damage.
However, it is not designed for prolonged exposure to water. So keeping it outdoors during a rainstorm could cause big problems for your washer.
Once you have your specific power washer, you can read the instructions to learn more about your washer’s tolerance for water. But in general, you should keep your washer stored in a dry place between uses.
You may also want to be careful about any power washer accessories you purchase. They will come with their own instructions, and you should verify that your foam cannon or power washer accessories are stored safely.