Minecraft bukkit permissionex permission file?

I run a bukkit server which I host in order to play online with my friends but I have come across a problem, I have the citizens/npc plugin and have been trying to set up npc traders but the problem is that only ops/admins are able to trade with them and not everyone on the server is mature enough not to abuse op/admin commands if given them. So in order to fix this problem I installed Pex/permissionex but I'm struggling to understand how it works as whenever I try to set up the permissions file myself it doesn't work how I would like it to as it either makes it so that everyone has op/admin commands by default or makes it so that you have to be an op to do anything at all.

So I was wondering/hoping if someone could write the file for me and possibly explain it aswell, the commands and abilities I would like regular users to have are:

The ability to break and place blocks (Basically to modify the world)
And the ability to interact with the npcs

/afk
/spawn
/back
/tpa
/tpahere
/tpaccept
/tpdeny
/sethome
/home

Thanks in advance

Added (1). Matt I tried you're permissions file but whenever I try and use a command as an op or non op it disconnects me from the server and displays the message "Internal server error" And the console gives a error report, which I can provide if needed

Here I wrote out some permissions. Also make you you have the plugin essentials. Please tell me if this worked or not!

groups:
Member:
default: true
permissions:
- modifyworld.*
- essentials.rules
- essentials.help
- essentials.pay
- essentials.balance
- essentials.tell
- essentials.sell
- essentials.back
- essentials.back.ondeath
- essentials.who
- essentials.afk
- essentials.list
- essentials.msg
- essentials.warp.list
- essentials.warp
- essentials.helpop
- essentials.motd
- essentials.spawn
- essentials.home
- essentials.tpa
- essentials.tpahere
- essentials.tpaccept

I suggest using GroupManager after all your still a beginner with permissions right?
Email me and I can send you my example of the permissions I have.
Make sure you have essentials downloaded.

Also you want to go to your Citizens/NPC website (Where you downloaded) And find the permission node area, for an example like worldedit right? You go onto the bukkit plugin place to download it right? So then you look for the permissions and then you write down "worldedit.*" In your permissions file.
So I can give you these abilities for you on here!

essentials.afk
essentials.spawn
essentials.tpa
essentials.tpahere
essentials.tpaccept
essentials.tpdeny
essentials.sethome
essentials.home

If you have any questions ask me!