I intend traveling to China on tour by applying for Tourist Visa L from my country Nigeria.

Hi Aremu! If you enter PRC once, you need a single entry type. If you need to enter twice, you need a double entry type. Before applying, you need to book tickets but don't have to pay. You can see whether the unpaid booking orders can be used to apply. If not, you need to pay before applying. In this case, if your application is not granted, you have to ask for a refund from the airline.