OLEDs and QLEDs use the same general idea: Power, light, and color sources. Exactly how the panels operate and get these sources is what differentiates them.
QLED screens use quantum dot technology to create images. It will give you enhanced color and detailing on-screen compared to its LED counterparts, but it's not "quantum" in any way -- that's simply a marketing catchphrase to separate if from LED. These TVs are more suited for bright spaces.
LED screens, on the other hand, use mini LED lights that individually light, creating true blacks and helping colors pop on the screen. Because it's not a cheap panel to produce, they're usually pricier. These TVs are more suited to darkened spaces.