You mean hooking these up to an amp, not the speakers. You still need an amp, and the amp needs a phono plug input, most are RCA. However, most new cars have this type of input so these are good for cars. However for cars you really don't need 5'. Two to 3' is enough.

unless he's talking about small computer desk speakers. But then, it would already have a 3.5mm male cable so you'd probably hook that up to your mp3 player directly

Yer a PITA.
Nothing wrong with what he put.