Help request - understanding code of decompiled wow binaries

[aviana]

Hello, I am a total beginner to disassembling executable files and reading memory etc., so I hope for some guidelines in using IDA.
I disassembled a 15050 version of the client and used the IDB provided by tom_rus, also managed to find the constructors and handlers thanks to info provided by LordJZ for each opcode.
My problem now is understanding where are those functions called and by whom, as well as how to interpret the parameters handed down to the function and the local variables used ?
Is there any reference source ?

for example:

// SMSG_WORLD_SERVER_INFO
<OpcodeInfo>
    <Opcode>17976</Opcode>
    <Index>300</Index>
    <Constructor>7087872</Constructor> 
    <Handler>9221296</Handler>
    <Destructor>6947648</Destructor>
    <Comment>Jam opcode, switch case is at 0x66745E</Comment>
 </OpcodeInfo>

If somebody could try to explain, as pointless or futile as it might seem to you, I'd really appritiate.
I read like last 5 pages in this section, but still confused, a solved example would do good. Thanks to whoever can help!