How do I make these planters form y entrance area?

You mean like this?

They make landscape blocks you can use to build the planters. Make the D shape on the ground and then go up. I would then put a heavy duty tarpalin inside the planters and fold over, cementing in place and add one more row of pavers on top to hold the tarp in place. Fill with potting soil and plant! Enjoy!

Use landscape blocks or bricks. Lay a hose on the ground in the shape you want then follow the outline when you place your blocks.

Before you start drowning your plants with a capital D, consider the origin of letters. All letters originated from Engineering Components Past. D is indeed a Component. Of a Boat. Before that improvement in around 40 BCE, D is yet a Boat made of a Hollowed out Log. t was the tool to hollow out that log. You should use a far more reasonable structure using p with q. Hence the origin of the phrase: "Mind your p's and q's". Trust me you do not want a 6 foot wide 3 feet deep D filled with Soil in the Rainy Seasons. Soil Absorbs Water only until it becomes mud after that Water Absorbs Soil.

Cut large animal water tanks in half. They come in metal or black rubberish. Add a back to them and then you can brick, paint, twig, etc the front. Don't forget to add drainage holes.