In order to create a Purchase Order within Tally, first this feature needs to be enabled.  This can be enabled in Settings> Purchase Order Options, then tick Enabled.  This will then turn any unpaid receipts in to Purchase Orders until a payment is made, it will then convert to a Purchase Receipt once cleared and paid.  This means in order to create a Purchase Order you will need to follow the steps for Creating a Purchase Receipt, but leave this as unpaid.  You may notice that creating a Purchase Order in this way results in it forming as a part of your accounts, which isn’t always correct. Ideally you could create a Purchase Order separate from your accounts.