What is SGST, CGST, and IGST? $ When is Tax Levied?

WHAT IS SGST, CGST, AND IGST?

Suppose goods worth INR 10,000 are sold by manufacturer A in Maharashtra to Dealer B in Maharashtra. B resells them to trader C in Rajasthan for INR 17,500. Trader C finally sells to
End User D in Rajasthan for INR 30,000.
Suppose CGST= 9%, SGST=9%. Then, IGST= 9+9=18% Since A is selling this to B in Maharashtra itself, it is an intra- state sale and both CGST and SGST will apply, at the rate of 9% each.
B (Maharashtra) is selling to C (Rajasthan). Since it is an interstate sale, IGST at the rate of 18% will apply.
C (Rajasthan) is selling to D also in Rajasthan. Once again it is an intra-state sale and both CGST and SGST will apply, at the rate of 9% each.
*** Any IGST credit will first be applied to set off IGST then CGST. Balance will be applied to setoff SGST.
Since, GST is a consumption based tax, i.e., the state where the goods were consumed will collect GST. By that logic, Maharashtra (where goods were sold) should not get any taxes.
Rajasthan and Central both should have got (30,000 * 9%) = 2,700 each instead of only 2,250.

Maharashtra (exporting state) will transfer to the Centre the credit of SGST of INR 900 used in payment of IGST. The Centre will transfer to Rajasthan (importing state) INR 450 as IGST credit used.
**Do note, that custom duties are not part of this
tax structure.

When is Tax Levied?

A taxable event such as manufacture, sale and provision of a good has to occur for tax to be collected. Under the current system, each taxable event is subject to multiple taxes such as excise, VAT/ CST and service tax. But under GST, products will no longer have multiple taxes, and will not incur excise duty as well as VAT at different points of time. There will no longer be any difference between goods and services in terms of taxation.
An example of this is when we go out to eat at a restaurant. Earlier, the customer paid both VAT and service tax on a single bill, but after GST is implemented there will be a single tax charge on the bill amount.
This leads us to an important concept in GST - Time, Place, and Value of Supply of goods and services. Let us look at these provisions in detail in the next chapter.