I hire items from my shop how do i enter those, and also sell items which i have entered already into inventory stock
Create (or rename) an income account for rental income. If you frequently hire out the same items, create sales invoice items for each to make things go faster, but this step is not absolutely necessary. Then create a sales invoice and select the appropriate sales item. Adjust the quantity and you should be set.
To sell an inventory item, see the Guide at http://www.manager.io/guides/inventory-items.