Registration requirement affects input tax credit availability; voluntary registration permits credit on inputs held before registration. Registration may be single for a State/UT with optional separate registrations for business verticals; registration liability arises on exceeding the turnover threshold and voluntary registration permits ITC on inputs and inputs in stock immediately preceding grant, subject to sections 16-18. Inter State supplies between distinct persons attract IGST; amounts payable by the supplier (e.g., transport) form part of transaction value even if paid by recipient. Branded packaged food in unit containers is taxable while unbranded bulk supplies are exempt. Tax invoices and bills of supply rules, credit notes for returns, composition ineligibility for liquor suppliers, and transitional restrictions on capital goods credit are also specified.