Hey welcome. Good news, there have been some posts about this. A quick search for “tree slice” finds this:
https://community.glowforge.com/search?&q=Tree%20slice
Read though these posts and you’ll get going in the right direction.
I will say that there are a few skills to learn about to get a good result here, you’ll definitely want to learn about engraving without the crumb tray. Again a quick search for “without crumb tray” will get you all the info you need.
Since you’re just getting started I’d suggest reading lots of the basics to get a solid start. The research time is well worth it.:
Have fun!