For creating purchase transactions like purchase order, quotations, purchase invoice and debit note, you'll have to add vendors

Create Vendor 

To create a new vendor: 

• Step 1.  Go to the Purchase module in the left sidebar and select Vendors menu
  
• Step 2. Click the Add Vendor button 
  
  
• Step 3. In the Profile page , fill in the requested details:
  
  
  
  
  
• Step 4. Click Save or Save & create a contact