The barter system is a type of trade that involves the exchange of goods and services without the use of money as a medium of exchange. Trade, on the other hand, is a broader concept that includes not just the barter system, but also, international trade, commodities trading, currency trading, etc. The main difference between barter and trade is that while barter trade does not involve money, other forms of trade occur with currency used as a medium of exchange. An important point to note is that the invention of trade whether barter or otherwise has developed a useful system under which individuals, businesses and nations can exchange or sell off the products or goods held in excess and purchase or obtain desired products, goods and services. The invention of currency has greatly simplified this process making trade convenient and fair.
When you load the menu option, the values you see displayed will be the values currently in use by your game. Vanilla values are 3.3 and 2.0. If the menu is displaying different values, then you have a mod installed which is already adjusting these two settings. If you choose to select a new setting, Trade & Barter will override the settings from the other mod. If at any time you wish to revert the settings back to those made by another mod, simply deselect this setting and reload your game. You will need to reload your game before the changes from Trade & Barter are fully canceled out.