'Creating a Jenkins job that works with multiple GitHub repositories

Our build system is complicated enough as it requires to compile various tools present on multiple GitHub repositories.
I understand by now all the Jenkins basics, but I am unsure how I could set up a single job that can do the following steps:

1.  Pull multiple repositories from GitHub
2.  Building whatever is needed on each repository (libraries, product firmware image)
3.  Run a bunch of tests on those outputs


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