Technically, I'd agree with fredbär's suggestion, which is exactly what I thought of for "Bestellschritt."
Practically speaking, however, you'll never see something like "Continue with the next step in the ordering process" on a webpage, because that is simply too many words strung together.
One thing you do see, at least early in the ordering process is something like:
"Proceed to (Secure) Checkout" or "Enter Secure Checkout" or "Checkout Now"
which might be followed by:
and then something like:
You also sometimes have:
"Add to Cart"
which can be followed by:
"View Cart and Checkout"