Normally ls doesn't print filenames that start with a dot. With -a, it does, but that includes . and .., which exist in all directories, and hence aren't very interesting. With -A it prints everything but those two.

$ touch normal .hidden
$ ls
normal
$ ls -a
./  ../  .hidden  normal
$ ls -A
.hidden  normal

In that if-statement, the command substitution $( .. ) captures the output of ls, and [[ -z ... ]] tests if it's the empty string. That is, that there's no files in the directory.

Usually, reading the output of ls is not a good idea, if you want to loop over files in the shell, you can just use *. Here, it should work, though, except for the fact that if the given directory name contains whitespace (or filename glob characters), they'll be expanded on the command line of ls, which may mess up the results.

See:

• https://mywiki.wooledge.org/ParsingLs
• When is double-quoting necessary?

Nothing related to bash. It tells ls to show all "hidden" files (those whose names start with .) except for . and .. (special directory entries representing the current directory and the parent directory, respectively).

Compare with ls -a, which shows all hidden files including . and ... The presence of those two entries in the output would make the directory appear to be not empty, even though it really is.

The ls -al command is a combination of ls -l (use a long listing format) and ls -a (do not ignore entries starting with .)

The result is a long list (the ls -l part) with (from left to right):

• filetype
• file permissions
• number of links
• owner name
• owner group
• file size
• time of last modification
• the name of the file or directory

while the ls -a means that hidden files are listed as well.

see also man ls (as always man is the first source of information), and this link.

A little more explanation on what you see

The output starts with the number of disc blocks, used by the directory (in your case 76). From the GNU docs:

For each directory that is listed, preface the files with a line ‘total blocks’, where blocks is the total disk allocation for all files in that directory. The block size currently defaults to 1024 bytes, but this can be overridden.

Then:

• the first character describes wether it is a directory (d) or a file (-) (or some other file type, see the docs for a complete listing)

File permissions:

• the permissions in a nine-character section (3x3 for owner / group / other users)

Links

• The number of links is the number of hard links to the file. For a directory, the number of hard links is the number of (immediate) subdirectories plus the parent directory and itself.

Owner

• name of the owner
• name of the (owner) group

File size

• You see many files with the size of 4096, which is the minimum size for a directory on ext3 and ext4.