Simply submit a tender with a bid through a broker, dealer, financial institution, or TreasuryDirect for the security you would like to purchase. You can bid either noncompetitively or competitively, but not both ways in the same auction. In TreasuryDirect, you can only bid noncompetitively.
If you bid noncompetitively, you'll be awarded the full amount of your bid for a security at the rate, yield, or discount margin determined at the auction close. Therefore, you don't have to specify a rate, yield, or discount margin with your bid. Noncompetitive bids are limited to $10 million per auction. Most individual investors bid noncompetitively.
If you bid competitively, you specify the return - the discount rate for Bills, the yield for Notes, Bonds, and TIPS, or the discount margin for FRNs - that you wish to receive. Depending on the highest competitive discount rate, yield, or discount margin awarded at auction compared to your bid, you may be awarded the full amount, a portion, or none of the security for which you bid. Competitive awards are limited to 35% of the total offering amount minus net long position.