Explanation:

Centre cannot impose any tax on goods beyond manufacturing (Excise) or primary import (Customs) stage, while states do not have the power to tax services.
State government has power to tax on sale of goods but centre has powers over tax on the production or manufacturing.
Once the GST Bill is passed, there will only be a national-level central GST and a state-level GST spanning the entire value chain for all goods and services, with some exemptions.
Centre can also levy Integrated GST for interstate trade.