Is there a way to create multiple directories at once with mkdir?

Short answer

mkdir takes multiple arguments, simply run

mkdir dir_1 dir_2

You can use lists to create directories and it can get pretty wild.

Some examples to get people thinking about it:

mkdir sa{1..50}
mkdir -p sa{1..50}/sax{1..50}
mkdir {a-z}12345 
mkdir {1,2,3}
mkdir test{01..10}
mkdir -p `date '+%y%m%d'`/{1,2,3} 
mkdir -p $USER/{1,2,3} 

1. 50 directories from sa1 through sa50
2. same but each of the directories will hold 50 times sax1 through sax50 (-p will create parent directories if they do not exist.
3. 26 directories from a12345 through z12345
4. comma separated list makes dirs 1, 2 and 3.
5. 10 directories from test01 through test10.
6. same as 4 but with the current date as a directory and 1,2,3 in it.
7. same as 4 but with the current user as a directory and 1,2,3 in it.

So, if I understood it correctly and you want to create some directories, and within them new directories, then you could do this:

mkdir -p sa{1..10}/{1,2,3}

and get sa1, sa2,...,sa10 and within each dirs 1, 2 and 3.