Well, seeing how many people lack knowledge in packet editing, i decided i should make this TUT to help you guys understand it a little more and know how to use it better.
First, a brief explanation about packets:

Your game client is communicating with the server with codes. those codes are basically the packets, which are based on HEX basis. Your client constantly sends packets to the server and of course, receiving packets from the server. Those packets are basically commands and reaction. For example, if you trade someone, you send the server a packet telling it that you have traded a person. If you receive a msg, be is whisper, to-all, buddy, guild, w.e, you receive a packet which is actually the msg.


Now, after understanding bit more what are packets, this is how you can use them:
First, as said, since the packets are based on HEX, the values they can hold are from 0~9 and/or A~F. each value is represented with 2 digits (00, 22, AA, BB, AB, 05, A3 and so on)
now, to be able to use and send those packets, you will need a packet editor. you can use any you like. Once you record a packet, you can play with it a little bit, you can change it, you can spam it, you can do many many things with it. lets take for example, a dmg packet. it is always good to take at least 2 packets and compare them to understand which part represents what
Code:
Code:
36 00 D7 5F 78 00 FF 00 A8 01 00 00 DC B7 3E 00 7C AF 48 00 01 00 00 00 00  36 00 9B 7D 78 00 FF 00 00 00 00 00 DC B7 3E 00 7E AF 48 00 01 00 00 00 00 36 00 77 83 79 00 FF 00 00 00 00 00 DC B7 3E 00 C0 B2 48 00 00 00 00 00 00  36 00 53 89 79 00 FF 00 A3 01 00 00 DC B7 3E 00 7D AF 48 00 01 00 00 00 00
Compare those 4 packets and the colored places and you notice the following:
the part in RED, constantly changes. a part that always changes in a packet is a TIME STAMP. most packet editor recognize the char "*" as time stamp. using this time stamp every time you will send a packet, the "*" char will be assign a new value, different (usually) than it was last time you sent it.
the part in BLUE, that is the dmg part, how can you tell, you just need to compare it with the dmg you have taken. as you can see, the 2nd and 3rd has 4 values of "00" that means the dmg was a "MISS". the 1st and 4th packet contains actual values, you can ignore the last 2 "00" because when you convert it, the number will remain the same. do note that the packets in maple are REVERSED. that means, in order to convert it properly you need to convert (when we take packet 4th as the example) "A3 01" as "1A3".
the part in GREEN, changes how ever repeats it self also. a time stamp is never in the middle of the packet, its always on the start, therefore this is NOT a time stamp. this is a monster ID. how to get that, well, you can record the packets with the header of E900 and compare the values there. (first 3 values after the header).

Ok, so we got a dmg packet, what can we do with it?
Well, specifically with a dmg packet, you cant do much, but few things you can do with it, is edit the dmg value to be, for example 0A AA AA AA, and you will receive 178M dmg. you can also edit it to 00 00 00 00 and get MISS. if you spam it you will see a lot of DMG appearing.

And thats it, using this knowledge you can record other packets, compare, understand what each part stands for, and edit. 1 tip you should do, record packets with values that you know that should appear to start the search. for example, if i buy a pot from the NPC, for the price of 50Mesos, ill know to look in the packet for the value "32", and the value "01" (because it was 1 pot), now since you most likely have more than 1 same value in a packet, you just (in this example) buy the pot again, this time you buy 2 pots for example, so total price will be 100 and amount of pots will be 2, so ill know to search for "64" (which is 100 mesos) and "02" (2 pots), comparing it to the other packets, i can conclude which part stands for what, and so on.

I hope this guide helped ya understand packets more and to understand how to use them, for any questions, feel free to post below ^^