The Atlantic Wall was not built all at once as a massive defensive line of thousands of bunkers. It was a construction process that lasted several years, starting in 1942 and continuing until the end of the war in 1945. Tens of thousands of workers from the occupied countries worked on it, some of them well-paid, others forced to work.
Because the Germans used standard designs for bunkers, planning and construction could be done quickly, since the required raw materials, resources, and labour time were already known in advance. You can compare the different types of bunkers a bit to IKEA building kits, but of course on a much larger scale. There were bunkers for soldiers, radar stations, artillery, ammunition storage, fire control posts, headquarters, and many other types. All components had been designed beforehand, and even the entire interior layout was predetermined. During construction, they knew exactly where beds, cupboards, stoves, telephones, and even periscopes had to be placed. With a periscope, a soldier could look outside from inside a bunker without having to leave it.
A bunker was not just a standalone structure; most were built in connection with other bunkers and so-called fieldworks such as trenches, dugouts, observation posts, and weapon positions. A number of defensive works together formed a “position,” or bunker complex. These were then connected with each other by tank walls, ditches, minefields, and other obstacles. This created a defensive line. In strategic areas, such as a port or an island, all positions together formed a Festung (fortress). One large system, defended from all sides, both against attacks from the sea and from land.
If you look at these defensive areas on a map as a chain along the coast, you realise that the Atlantic Wall was one large interconnected defensive system.