A skill has to be linked to at least one job, education entry or certification, so choosing where you used or earned it is required. Resumes and cover letters list a skill only while it has a link that is not hidden, so the link is also what puts the skill on your resume. Pick a category and proficiency level, then check off where it applies.
You can link the skill to more places later from the link icon next to it, and hide it for any one of them without removing the link.
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