When does my stock on hand for an item increase?

When stock on hand is calculated using shipment orders and receives:

The stock in hand for the items in your inventory increases when a Receive(purchase receive) is created for the items delivered to you by your vendors.

When stock on hand is calculated using Invoices and Bills:

The stock in hand for the items in your inventory increases when a bill is raised for your items. Bills can be raised from purchased orders in ‘Issued’ status, from purchase receives or you can directly create a bill for your vendors.