I have had to edit your question because your original question contained multiple questions, which is not permitted under eNotes regulations.

This story of course contains the narrator's attempt to commit the perfect murder. He comes up with a plan to dispose of the corpse in such a way that nobody will ever find the body of his wife and therefore accuse him of her murder:

Finally I hit upon what I considered a far better expedient than either of these [other plans]. I determined to wall it up in the cellar--as the monks of the middle ages are recorded to have walled up their victims.

Thus the wall that he creates is literally and symbolically designed to conceal his guilt and act. As the narrator completes this task, and goes to much effort to make sure that it is done successfully, it is clear that he has done his job well:

The wall did not present the slightest appearance of having been disturbed.

So, the wall then seems to operate symbolically as the attempt of the narrator to conceal his actions and to get away with his crime. However, as the narrator in "The Tell-Tale Heart" likewise discovers, such crimes are not easily walled over, and fate, or conscience (depending on how you view the black cat) has other ideas, showing that in spite of the narrator's efforts, his crime will not be walled up and concealed so easily.