Newbies: assembler is a low-level programming language, if you want to program on an even lower level it's just bits and bytes.

These days you might think assembler is dead. Modern compilers can produce faster code than assembler written by hand. Only real assembler pros can write faster code.
So why learn then?
When writing high-level code you are limited by the language itself. When writing assembler you are limited by the computer you use.
Assembly programs are quicker and smaller then others.
It is best used to optimize programs written in high-level languages, be it on their size or on their execution.