Unlike depositing liquidity to existing pool, for newly created pools, you need to enter token amounts for both sides of the pool. The proportion will define the initial exchange rate for this specific pool.
Once you type in any amount, typically DeDust will automatically add another token amount, based on the existing exchange rate on the market. Toggle the Lock rate, if you want to set own initial exchange rate.
1) DUST amount input
USDT amount auto-input
2) USDT amount input
DUST amount auto-input
For newly created tokens, with no pools and market rate yet, you have to enter both amounts, in any case.
Once Lock rate option is deactivated you can type in both amounts manually, in proportion you need.