This is probably a really dumb question but I can't figure it out. I'm new to Inkscape.

I created a sunburst from triangles, and I have a rectangle shape behind it. How do I remove the sunburst parts that extend past my rectangle? I only want the sunburnt to show inside the rectangle, not beyond it.

Seems simple but I'm lost lol
I can submit a pic if needed

You could group the sunburst and clip it with the rectangle.

Also keep in mind that you can define the area that gets exported to a png.
For example the canvas can be used as a bounding box for the exported area. Or a selection.