Hey Rafiq,
Thanks for your post and welcome to the QuickBooks Community!
Create your items as Stock, when entering the item details there is an option to enter 'Purchasing information' where you enter the purchase price.
For the second-hand stock which is not purchased, enter the purchase amount as 0.00, which will post 0.00 to the Cost of sales when recording a sale transaction.
You can see more on setting up stock in QuickBooks on our guide here, and you can post any further questions below :)