Im having issues understanding and solving this error: cannot open source file “juce_core/juce_core.h” in JuceHeader.h — the modules are missing from the folder. … i recently downloaded juce on a new computer and when i try to export to ide it just opens a sln file. I think it has something to do with that.

Have you checked that your JUCE paths are valid? In the Projucer go to Projucer->Global Paths. In the settings window that pops up your path to JUCE needs to point to the main JUCE folder and the JUCE modules setting needs to point to the modules folder within the JUCE folder

this is how i have it confingured. Im not sure why its not working… thanks for the help!

You need
1/ to set the path to JUCE folder,
2/ use that global path for the JUCE modules.