Intrastate transfers or supplies are not taxable if supplied within same registration.
However interstate supplies are charged IGST.
For example, if you transfer goods from one branch located in Maharashtra to another branch located in Maharashtra then no need to charge tax and goods can be transferred with a Delivery Challan. Condition is that both should be registered under same GSTIN.
But if you transfer goods from Mumbai to Surat branch then you need to transfer good with a tax invoice by charging IGST.
However Surat branch will get input tax credit of tax paid.