“Upload CV” means the employer or college wants you to attach your CV file to your application. If you’re applying for work or college admission in the US or Canada, a CV is the same as a resume: a 1–2 page document that describes your relevant experience and skills.
But if you’re applying to an overseas organization — or if you’re looking to work in academia or medicine — you may need to upload a CV that includes enough pages to describe your academic and professional career in greater detail.