There are three ways to willingly become a creditor of the U.S. government; buy Treasury Bills, buy Treasury Notes, or buy Treasury Bonds.  Treasury Bills, often referred to as T-Bills, are U.S. government debt issued for less than one year.  They are issued at a discount to par, so interest is paid when the principal investment is returned. Treasury Notes are government debt issued with a maturity of 1-10 years and pay interest semi-annually. Treasury Bonds, sometimes called T-Bonds, are U.S. government debt issued with a maturity date of more than 10 years.   T-Bonds also pay interest semi-annually.

Interest rates on government debt are not protected against inflation. To satisfy investors who are worried about the risks of inflation, the treasury sells TIPS (Treasury Inflation Protected Securities).  TIPS are available for both Treasury Notes and T-Bonds.  With TIPS, interest rates increase during periods of inflation, as calculated by the consumer price index.
 
Investors can buy government debt directly from the government.  To do this, however, an investor must buy thousands of dollars worth of one issued debt instrument.  Government bond ETFs offer investors a way to diversify their portfolio without having to purchase thousands of dollars worth of government debt and without having to commit money for a specific amount of time.