To transfer stock, click on Products -> Stock Transfers in the side-menu. You'll be brought to a list of past stock transfers.
To create a new stock transfer, click on New Stock Transfer and you will see the page below.
You will need to:
Select whether to transfer or Add/Take Stock.
If you are transferring stock, select a source stock location and a destination stock location, and if you are adding/taking stock, just select a destination stock location.
Select the account the stock transfer should be categorized in.
Select a product to transfer or add stock for, and specify the quantities you would like to transfer/add.