Well, maybe. If any of this is confusing, see the Resources section at the bottom.
Quick terms (might differ a bit from other sources):
- "T-bills"/"treasuries"/"bonds" (there are multiple types) = a promise (from the US government) to repay an amount of cash at a specific future date, with interest. These are not intended to be used as money to buy goods/services, but are a mechanism for "the fed" to manipulate interest rates, the amount of cash flowing through the economy, and the amount of cash that the government has to spend on things.
- "Reserves" = cash (typically cash that a bank actually has).