A trade surplus is when a country's export revenue (the money they get when they export their G&S) or credits, is greater than their debits (the imports they purchase that arrive in their country).
Therefore, when a country is experiencing huge trade and current account surpluses, they can use that revenue to pay off their overseas debt, which contributes to acheiving external stability. Remember, the more money a country has, the better off it is as it can purchase more imports, borrow with ease from other countries as they have the money to pay them back, so the more G&S a country can export, the more ecenomic growth they experience. There's also an improvement in the TOT.