There's not much to making them. A switch is either ON or OFF, like a light switch. And you control when to turn them on or off (with the event command Control Switch).
You can then condition events on switches. For instance, when you make a new page, there are two checkboxes for switches. If you enable them and select a switch, it means it won't run that event page until those switches are on. As a rule, an event will only run one page at a time and it checks from the last one to the first. In the screenshot, it would run that event page only if switches 1 & 2 are ON. If either one isn't, it would run Page 1 instead. If Page 1 had conditions that weren't met, it wouldn't run any page.
Another way you can use switches is through the event command Conditional Branch. In the screenshot, if Switch 3 is on, then it would run the stuff right under it. If Switch 3 weren't on, it would run the stuff in the else branch.
There are a lot more detailed tutorials for events though. Just check out the databases. Constance has a great tutorial for new users generally too.
(For what you wanted to do, you'd make two event pages. The first page would be autostart and it would have the Set Weather Effects command, then it would have:
Control Self-Switch: A ON
On the second page, you would checkbox self-switch A is ON in the Conditions box. That's it.