How is this lasagna pasta supposed to be cooked?

For the Pasta : You just lay them as-is in your baking dish.

No need to pre/par cook them.

For the rest of the question: The icons seems to refer to steps in a recipe which should be printed out on the box.

The 0.9L is the same as the 900g of milk listed in the linked recipe.

The steps looks to be a really minimalist description of the recipe.

Barilla say their lasagne is no-cook (not all lasagne is), so I can only assume they expect you to make your béchamel with 900ml milk, then use a jar of their bolognese sauce in the alternate layers. It's a tad lacking in precision, for sure.

Personally, i'd just search a no-cook lasagne recipe online, as the liquid balance is pretty important for lasagne - too much & it's like soup & slime, too little & it's a brick.

I just checked Barilla sites & recipes around the world, most Barilla is no pre-cook - it also says that on your box - only their wavy lasagne is pre-cook.

I found written instructions for how to use this pasta on the Barilla website. They are pretty much the same as you have interpreted the iconic instructions, which is to say, it's not a full recipe.

COOKING YOUR PASTA

1. Boiling is not necessary for Oven Ready Lasagne.

2. Add contents of package directly to baking dish and add Lasagne, sauce and filling.

3. Alternate layers with Lasagne, sauce and filling until desired number of layers is achieved. Bake according to recipe directions.

4. Lasagne may be prepared up to 24 hours in advance without baking it. Prepare and store the Lasagne in the refrigerator at or below 40°F. Since the Lasagne will be cold it will require a longer baking time, approximately 60 minutes at 375°F.

5. To freeze Lasagne, we recommend that you do not bake it before freezing. You may assemble the Lasagne in a freezer safe/oven safe container, cover tightly and freeze. When you are ready to bake the Lasagne, defrost it in the refrigerator for 24 hours. Bake it at 375°F and increase bake time to 70 minutes.

On a separate page with "tips and tricks" for preparing lasagne, they have these instructions for using the precooked lasagne sheets:

Barilla Oven Ready Lasagne sheets make assembling this classic pasta dish uncomplicated. For the best results, we offer the following tips for assembling your lasagne:

• Begin with a 13 x 9 x 3-inches deep baking pan, sprayed with nonstick cooking spray.
• Spread 1 cup of sauce on the bottom of the baking pan and begin layering.
• Place 3-4 sheets of uncooked Barilla Oven Ready Lasagne side by side on the bottom of the pan. The lasagne will expand to the edges of the pan during baking.
• Top with filling or sauce as directed in your recipe on every layer, spreading each to the edges of the pan to seal in and cook the lasagne during baking.
• Repeat this process for a total of 4-5 layers.
• The final layer will be 3-4 sheets of uncooked Barilla Oven Ready Lasagne plus the remaining sauce and cheese, if included in recipe.

They also have these Q&As:

Q: I am using my own homemade red sauce, the recipe on the back of your box does not indicate how many ounces of sauce this recipe requires.

A: Our recipe requires a minimum of 48 ounces of sauce. It's important to have enough sauce to ensure the lasagne is moist and rich.

Q: If we wanted to use the Oven Ready Lasagne with a cream sauce, how much sauce will it require?

A: We believe a minimum of 6 to 8 cups is necessary.

These Q&As seem to refer to the 9oz (255g) box size available in the US. So for your 500g box, you would want double the recommended amount of sauce. For red sauce, use at least 48 oz (1.4 L) of sauce for 255 g of pasta or 96 oz (2.8 L) of sauce for the full 500 g box. For white sauce (bechamel sauce), use 1.4 L to 1.9 L for half the box, or 2.8 L to 3.8 L for the full box.

Barilla provides several recipes for their pre-cooked lasagne sheets here.

I have the exact same visual instructions on my pack of lasagna sheets, except that they come with a full recipe as well.

10 sheets of lasagne
Ragout: 400 g minced beef, 40 g chopped onions, 100 g diced carrots, 40 g chopped celery, 30 g tomato concentrate, 40 cL water, 4 tablespoons extra virgin olive oil, 80 g grated Parmigiano cheese, 1 bay leaf, salt and pepper.
Béchamel: 0.9 L of milk, 50 g butter, 50 g flour, nutmeg, salt

1. In a saucepan, fry the onion in the oil, celery, carrot, bay leaf, and the minced meats until brown.
2. Add the tomato concentrate and water, season with salt and pepper and cook for 20 minutes on a medium heat. For a simple Bolognese sauce, after sauteing minced beef in a pan, add Barilla Napoletana sauce and heat.
3. Melt the butter in a large saucepan, then the flour and all the previously boiled milk. Whisk the mixture while adding salt and nutmeg and bring to boil.
4. Grease an oven proof dish and spread a ladleful of béchamel and 4 tablespoons of ragout on the base, then cover with 2 sheets of lasagne.
5. Repeat the previous step 4 times, forming 5 layers. Make sure you cover the corners of each sheet with plenty of béchamel and ragout sauce. Sprinkle 15 g of grated Parmigiano Reggiano cheese on each layer.
6. Bake in a pre-heated oven at 220° C for 20 minutes. Remove from oven and leave to rest for 10 minutes.

It’s no-cook pasta, meaning you do not need to cook the sheets of pasta before putting them in the oven.

Basically, you alternate one layer of béchamel (just enough to cover the bottom of the baking dish), one layer of (uncooked) pasta and a layer of ragú (again, just enough to cover the pasta). Repeat until dish is full or you run out of one or more ingredients. Sprinkle grated cheese on top and bake for 20 minutes at 200°C.

Of course, you can replace ragú with any other tomato-based sauce.

In order for the finished product to stay firm and not run away, the texture should be thick/creamy rather than liquid. Also, you can adjust the thickness of the layers of sauce to match its firmness: thin enough so you need to spread out the sauce manually rather than just pouring it until everything is covered.