The only things that a CPU understands are opcodes.
Opcodes are numbers which are related to CPU functions (e.g. : load a value into a CPU register, add registers, shift bits, compare registers/memory values, jump to memory, etc...).
So the lowest level language is the machine laguage (opcodes) and as it would be difficult to write programs using only numbers, the assembly programs provides the use of mnemonics which is a concept that allow to write understandable code and to compile programs directly in ML.
So, for example, rather that to write 45 DF 20 32 50 (random numbers here), it's easier to write :
XOR AX,AX
ADD AX, BX
CMP BX,CX
etc...
To go further into the knowledge of all the higher level languages, I suggest you to use wikipedia which profides enough informations to get familiar with the different concepts.
Here is a good page to Start :
http://en.wikipedia.org/wiki/Interpreter_%28computing%29Look at the "See Also" section of this page which links to :
- Command-line interpreter
- Interpreted language
- Compiled language
- Dynamic compilation
- Partial evaluation
- Meta-circular evaluator
I think you'll find a lot of answers to your questions there.
Have fun as it is really exciting to discover the universe of programming languages!
Cheers.
(PS. Sorry for my bad English).
