I'm confused which w3wp service should i choose to debug SP solution, what's the purpose of other services
Attaching to multiple processes, while it will work, is a bit overkill and attaches unneeded processes.
Look up the name of your app pool in IIS, open up a command prompt and then enter
cd %windir%\system32\inetsrv\ appcmd list wps
(or appcmd list wps /apppool.name:AppPoolName if you know your pool name and want to be specific)
Your app pools will be listed there along with the process ID. You can also go to the root of your IIS and select Worker Processes and look for your app pool's PID there.