A government bond pays fixed interest and returns its face value at maturity. Its yield is the return implied by today's market price. If the price falls, the fixed payments are worth more relative to what you paid, so the yield rises.
The 10-year yield is the benchmark for long-term borrowing costs, and the 2-year yield closely tracks where the market expects the policy rate to be.
Why it matters
Yields bundle three things: expected policy rates, expected inflation, and a term premium for the risk of lending for longer. Rising yields raise mortgage and business borrowing costs and make shares relatively less attractive, because safe bonds pay more.
See the data: Australian 10-year yield, US 10-year yield.
General information, not advice.