What is GST E-way bill and why has it been preponed

GST has brought much required transparency and accountability to the market and E-way bill is one of them the process and procedural aspects of GST that the movement of goods are prescribed in the e-way bill rules. E-way bill stands for Electronic Way Bill. It is a specific bill that is generated for the specific consignment involving the movement of goods. However, the e-way bill implementation was supposed to be rolled out through nationwide from 1st April, 2018 but at the recently concluded 24th GST Council meeting it has been passed from the 1st of February, 2018 – a full two months ahead of the earlier plan. The e-way bill GST provisions had primarily targeted a single national level e-way bill, which could be used by suppliers and transporters all across the country. Before when there was no such bill the States were authorized to continue their own separate e-way bill systems. However, the GST Council received several complaints and representations from the trade and transporter communities, stating that this was causing an unnecessary chaos to the inter-State movement of goods, prompting the need for an earlier implementation of the e-way bill. As a result the GST Council, reviewed the readiness of the hardware and software required for the nationwide roll-out of e-way bill, and announced it swiftly.

I-T dept tells traders to use e-way bill (GST) to sell goods, but what is it and why has it been postponed?

Debatably, the GST E-way bill is a form of electronic document that can be used by individuals and businesses to carry out their transaction of interstate trade. Briefly explained, when an inter-state trade is performed, a bill of supply must be filled out and served electronically to the concerned states in which the supplier and receiver of goods reside.
The E-way bill helps you to keep track of your deliveries by keeping a record of such transportations. This will, in turn, help you stay compliant within the stipulated time period.
E – way Bill is compulsory for interstate transportation of goods for B2C (Business-to-Consumer) and B2B (Business-to-Business). It doesn't matter if you're a buyer or seller.