A guy told me once when I asked that question "Its just metal, if you F it up, just cut another piece and do it again"
Words of wisdom from a 60+ welding guru, but not too comforting nor inspiring to someone that has never done it.
I am currently working with a friend who knows how to do this.
Learn from those who know. Plus, I dont have the tools to do metalwork and that makes a big difference.
My advice is to find someone that will do it on the side and let you help. It is the only way to learn.