To soak something is to submerge it into water. Before you cook dry beans, you soak them overnight first. If you’re not a bean, you can also soak up a cool experience by immersing yourself in it.
You can soak your dirty laundry in soapy water, or soak rice before you cook it, and you can also soak in a bubble bath. When you do this, you give these things (including yourself) a soak. Informally, the verb also means "immerse in an activity or experience," like when you soak up the applause after your masterful violin performance.