Using sniffed packets

Hello,

To start off, I am proficient in Java and have a general knowledge of programming, so please don't instantly discredit me.

I would like to make simple bot in Java, and need some help with packet analyzation.

Take for example a sitting packet:

Code:

[C -> S][704F]
04

With this data, I assume the 'opcode' is 704F? Then what is 04?

Then I noticed this packet is when you click on the ground/object

Code:

[C -> S][7021]
01                                                
98 66                                             
CD 04                                            
9F FF                                             
E9 06

7021 is the ground click opcode, yes? Then, what is all this extra data below? I assume coordinates of the click?

I also read of about security data, that is sent with each packet..

I am basically asking if somebody could break packets and their data down for me. I already have a bot gui/framework built, just need the packet implementation.