Great question! On Shopify Basic, checkout customization is quite limited without apps — you can tweak basic branding like colors, logo and font under Settings → Checkout but deep customization like custom fields, reordering steps or flow changes is unfortunately locked behind Shopify Plus.
Without apps and without Plus, your best free option is using Additional Scripts in checkout settings to add small CSS tweaks for design adjustments.
Falls Sie Schwierigkeiten mit den CSS-Einstellungen haben, lassen Sie es mich gerne wissen, ich könnte Ihnen helfen.