I would say the most useful thing I could tell a novice homeowner looking to learn something usefull is how to check the trap on a clogged sink drain. The trap is the "dip" in the pipes underneath the sink. It can catch large object and "trap" them before they go down the drain. It also serves the purpose of forming a barrier full of water so that the odor from the drainage system does not filter back up through the pipes.
On most sinks these days, you can easliy remove the trap simply by turning a valve on the two side of the trap and pulling it out. Make sure you don't spill it as you take it away.
Now do whatever you need to to clear out the trap before putting it back. See if you can find any diamond rings.