Go into Orders -> New, look to the right-most side and you will find a Create Order button.
After pressing it, a new window will pop up.
In there you can either Search for Existing Customers using the search bar at the top left (selecting an existing customer will pre-fill all Customer and Billing details).
If it's a new customer you will need to fill in all the details manually.
With all the customer information filled in, you can then start adding your Order Items. You can search for these either via Product Name or SKU. You can always add more items to the tabs below and delete them by clicking the minus icon on the right.
The Price and Tax fields will pre-fill automatically, but you can change them before creating the order, same as any flat Discounts you want to subtract.
By pressing Add Shipment on the bottom left side of the window you can add shipment details to this order.
After you're done adding order Items, you can leave a Note for the order.
With all of the information filled in, press Create Order and you're done.
Please Note: After orders are created they cannot be edited anymore, if you made a mistake you would need to change the status of the order to Cancelled and start again (cancelled order item stocks will return to inventory). Orders cannot be deleted, so they will remain in the Cancelled tab.