Death Stranding Amelie beach?

Question

How did Amelie appear and then bring Sam to the Beach? What does she mean by "So long as you have a body to return to, you can’t come and go as you please…"?

Answer 1

I believe the Beach, in this case, is largely in Sam's head as Amelie communicates with him on the Beach in a dream while he's sleeping. As to why there is an adolescent Sam there, and why she makes the comment about having a body to return to, that's tied up in revelations late in the game about Amelie's and Sam's nature.

Bridget Strand, the sixth extinction entity, developed uterine cancer in her early twenties. During surgery, her "ka" and "ha" separated, with her "ka" woke up on the Beach. Strangely, both halves of her essence were aware of each other's existence and worked in tandem. Due to the timeless nature of the Beach, Bridget's "ka" did not age, and the age gap between the two became noticeable. Eventually, rumors began to spread of a younger version of Bridget wandering the White House, and in order to deflect suspicion, Bridget created the persona of Amelie for her "ka", fabricating a cover history.

(this following bit is very much endgame material)

.... When John hesitated, Bridget decided to pull the trigger herself, but accidentally killed the BB along with Cliff. Feeling immense guilt at killing the baby, Amelie found the child's body on the Beach. She restored him and sent back to the world of the living, where Bridget then chose to raising him as her own child and naming him Sam, making him a repatriate in the process. However, in doing so, she upset the balance of life and death, and set the Death Stranding in motion. During Sam youth, as a sufferer of DOOMS, he had severe nightmares and would find himself stranded on the Beach unable to find his way out. Always there for him in such moments, Amelie would arrive to calm Sam and help him make his way out. At some point Sam fashioned a quipu for her in the world of the living, and was able to bring it with him to the Beach, where he gifted it to Amelie as a representation of their bond. However when Sam left Bridges, caused by the suicide of his pregnant wife and the relative voidout, Amelie loses the only true connection to the outside world.

The short, less spoiler, explanation is that both Amelie and Sam spent time on The Beach when he was young, and it's tied to his status as a Repatriate, where he visits the Beach in death, then is returned to life in his body.