The Journal Entry form posts the same double-entry lines as a paper journal. Choose a date and journal number, select an account on each line, and put an amount in either Debit or Credit. The running totals show whether the entry balances. Save only when the difference is zero. A line with amounts in both columns must be corrected before saving.
Customer and vendor detail also matters. A line to Accounts Receivable needs a customer, and a line to Accounts Payable needs a vendor, so subledger reports can identify who owes whom. Use sales and purchase forms for routine invoices and bills. Reserve journal entries for opening balances, corrections and adjustments that require direct ledger postings.