Do I need extra speakers for a Lenovo k430 desktop

If your monitor has its own speakers and your happy with the quality then no. I don't know of any desktop that comes with speakers other than the silly internal speaker that's basically for error beeps. 2.1 speakers can be fairly inexpensive and beat monitor speakers into the ground. Plug them into the green line out in the back. They range between $20 and $75 and even higher if your wealthy and like to splurge a lot. Having a wired remote is cool too so you can bring the adjustments forward instead of reaching back to one speaker to turn them up or down.