Default listing duration: When you create a new listing this option will default the listing duration to this setting. Some categories may not have your setting option so you will need to set these manually. For example if you set this to GTC (Good Till Cancelled), some categories do not have this option. The same is also true for some sellers who do not have an eBay shop.
Payment instructions: This is the payment instructions that you would normally type in next to your accepted payment methods in eBay. This text will rarely change so its good to have a solid payment instruction that can be reused over many listings. You can still edit this for each listing if required but it will default to this originally.
PayPal email address: eBay requires sellers to offer PayPal in thier listings, this setting is the default payment email address that you use to accept the PayPal payments. You can change this in the listing page if needed but it will default to this value originally.
Payment options (multiple types): Based on your country or eBay marketplace there will be different payment options you can offer your customers. You need to go through the options here and enable them if you accept that payment method. For manual payments such as PO or Cheque you should include the payment name/address in you payment instructions section too. You can still enable or disable the payment methods you accept on the listing page.
Immediate payment required: If you only offer PayPal as a payment option you can choose to require buyers to pay immediately. This will remove any buyers that commit to buy but do not pay as the order will not be confirmed until the payment has cleared through PayPal. You cannot use this option if you offer other payment options. This option can be enabled or disabled on the product listing page.
Tax included in listings: eBay only displays the Gross price to buyers. Here you can set the tax value that is included in your listings for when the order is imported to your store. This value is also used to display the net and gross price when you list an item to help you see both values. You can change this value when you are listing an item if the product has a different rate of tax.