These are often confused, possibly because two of them are relatively rarely used.

Cite means to refer to a source, as when you write a research paper.

Site refers to a specific place or location, as in a building site.

Sight refers to seeing, as in vision.

Examples:

• You need to cite more sources for your research.
• The accident caused him to lose his sight.
• We need to choose a site for the picnic.