Good to see you here, bansal-shubham05.
Let me share some details on how to manage inventory in QuickBooks Online.
Please note that there are some features that aren't available in the mobile app if this is what you're using. One of those is the inventory. Though we can add products, we're unable to set it up as inventory.
If what you're referring to is the QuickBooks Online Desktop App, it has the same interface and features with the browser version. However, the inventory is only available in QuickBooks Online Plus and Advanced.
You may check this link on how to add inventory products in QuickBooks Online for your reference. This link will show you more details on how to handle inventory.
Comment below if you need more help. Stay safe!