What is the differences between programming languages and generations 1-4

The same differences between spoken languages and dialects.

Programming languages have many differences, based on their generation, as well as their many design choices - how they handle typing, their syntax, etc. Due to the lack of a clear taxonomy, it is very difficult to compare languages directly. Wikipedia is a good start, though, with a solid article related to programming languages: Programming language - Wikipedia, the free encyclopedia

Regarding the first to fourth generation portion of your question, AFAIK it goes something like this:

• 1st-gen would be machine code (in other words, binary) - back in the day, simple computers would be programmed by flipping switches each equating to one or zero;
• 2nd-gen would be assembly - simple opcodes targetted at a specific CPU architecture's instructions;
• 3rd-gen would be languages with predefined types, structures, libraries, whose source code is compiled into machine code via single to multiple passes of a compiler (e.g. C, Pascal);
• 4th-gen would be languages that were (or might be) compiled and converted into machine code on the fly - scripting languages used by an application/parser (e.g. SQL, PHP, Python, etc).

All of this is off the top of my head, so if a more formal description exists, everyone feel free to correct me. :)