Although I'm 100% sure at least most of these questions have been answered more than once on this site and tht you have not bothered to look around.. I have nothing better to do right now so I will help you out.
1) Just have a look around to see what you can and cant do, including but not limited to moving/placing static objects (buildings, fences, barbed wire, etc.), moving spawn points, changing gameplay mode, adding global spawns, ADDING/TWEAKING/MOVING spawnable items, swapping players kits, changing/editing projectiles, removing out of bounds, editing terrain, changing points and plenty more.
2) After extracting the files you need making your neccesary changes and saving, you will go back into the win.rfa program press the pack button, select your modified file and then save it as either 001, 005, 008... etc. whatever you want and this will cause it to patch over but not replace the original. (By the way, I suggest only including the files you have edited, speeds up packing and is less to deal with!)
3) If you are unable to start the game (kicks you back to desktop right after the BF 1942 screen) you most likely packed it up wrong, check this out:
viewtopic.php?t=1854 ALSO; make sure you are packing the complete file, meaning it must be called bf1942- if you just try to pack the level file up the game won't start!! It should go Bf1942 - Levels- *Level name* - Game files
4) Ok for your problem I'm not sure, but did you move any control points? If so there could be your problem. In the past I have tried moving a control point to the secret airfield in gazala and it turned out not being server side (not letting people in)
So in conclusion I suggest you take a better look around the site and try working through the problem more. If you need more help I'm bored out of my mind so post up!