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. The Price and Tax fields will pre-fill automatically, but you can change them before creating the order. You can always press Add more items the the bottom left side of the window.
After you're done adding order Items, you can leave a Note for the order, enter the Shipping Price and any flat Discounts you want to subtract.
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 mistake you would need to Delete the order and start again (deleted order item stocks will return to inventory)