Don’t bother with Treasuries if you’re just a average guy with a few thousands or tens of thousands to invest. You can get better rates then TreasuryDirect by simply driving to your bank and getting a FDIC insured CD.
The best option for you would be a bond index fund. You can withdraw your money from one easily compared to holding the bonds yourself. Since most bond funds buy from the same pool of bonds the major difference will be how much they charge you. Index funds kinda win by default here through their low expense ratios. I am assuming you’re interested in buying (mostly government) bonds for safety. If you want bonds with higher yield and higher risk then I can type some more about them in another post.
I recommend getting a online account at Vanguard and buying into their bond funds. They have a Total Market Bond Index Fund which is IIRC 70% government bonds and a mixture of short, intermediate, and long term. Once you learn more about this you can sell and redistribute your money into the other bond funds. They also have tax exempt municipal bonds, GNMA, corporate, junk bonds, etc.