First off, welcome to the Z3 forum.
There are many things you should know before diving in.
The number 1 rule to modding is MAKE A BACKUP!
Your best friends in this forum will be the Search function, the Guides section and the Z3 Bible. The Bible has most everything you need to get started with your Z3. If you are ever unsure of what you are doing or what you need to do. Please post. We are all here to help.
Most everything you will need is in the Downloads section.

Read, Search, Ask, Learn THEN Mod!