Shipping Presets are a great way to apply shipping options such as package type or dimensions to your orders in ShipStation. Simply select the order(s), and select the Shipping Preset from the Shipping module on the sidebar, or you can set up hotkeys to apply these to your orders, such as Ctrl+G.
To set up a preset, go to the order drawer on the order sidebar and click Apply Preset and then Manage Presets.
Next, on the Shipping Presets popup, click + Add a Preset (In this example, I'll be setting up a First Class Mail Package preset with a hotkey of Ctrl+F).
Here, you'll be able to set up the preset's name, actions, and hotkey (Keep in mind that any actions not filled out won't apply. For instance, if you don't want to apply a weight with a preset, don't click the Weight checkbox, and the order's weight won't be impacted).
Now, the preset will appear in when you click Apply Preset or via the hotkey setup Ctrl+F.
If you ever want to edit or delete your preset, you'll have the option to when you select Manage Presets.
Once you get these set up, you can go back to this Manage Presets popup to print out the hotkey to a barcode. This way, you can scan for future orders.
Here's how this one looks on the 8.5"x11" page that it prints out on.