The shortest path from signing in to dispatching your first sales order.

Open Inventory → Warehouses and add the physical location you store stock in. Most small businesses start with a single warehouse. You can always add more later.
Go to Inventory → Products → New. Capture SKU, name, unit of measure, GST rate, and reorder level. The SKU must be unique per organization.
From the product page, use the 'Adjust stock' action to set the opening quantity in each warehouse. Adjustments write to the stock ledger so you always know where numbers came from.
Sales → Customers → New. GSTIN is optional but lets the system auto-apply IGST/CGST+SGST on invoices.
Sales → Orders → New. Pick the customer, add products and quantities, and save. The order is in DRAFT state until you confirm it.
Open the order and click 'Dispatch'. Stock moves out, an invoice is generated, and the order moves to FULFILLED.