Why do we need a resistor with LED flood lights?

The resistor can limit the current in the LED to a safe value. The voltage and the current in a resistor are linearly related. It means that a change in voltage will produce a change proportionally in current.

How to convert halogen lights to LED flood lights?

If you are looking for a softer light source at your place, LED flood lights generate low-intensity light and also more efficient of power than halogen bulbs. It is possible to convert a regular halogen light with an LED flood light with the appropriate tools and patience.