On the "Payment Amount" tab you can calculate a matrix of potential periodic payments for a given loan amount while varying the term and interest rate for the loan.
The "Loan Amount" tab allows you to calculate a matrix of various loan amounts that can be borrowed for a given payment amount for different terms and interest rates.
The "step values" on either tab control by what amount the interest rate and term are going to increase.
Note: It is not necessary to clear one calculation before doing the next. You can change one value and recalculate.