Electromagnetic waves move at the speed of light c, as reflected in this
formula:
c = f x
.
wavelength is the DISTANCE between two points on the wave the are the same --
between two crests, or between to troughs, or similar middle points, etc.
-- "the distance between any two points of constant PHASE," technically
frequency is how often complete wavelengths moves past an observer --
"the INVERSE of the time between points of constant phase" in jargon again
a DISTANCE, multiplied by HOW OFTEN you travel it, is a SPEED, in meters/sec,
as this analogy with trains might illustrate:
By analogy, crests of long wavelength light pass observers more slowly,
and crests of short wavelength light pass more quickly.
LONG WAVELENGTH implies LOW FREQUENCY
SHORT WAVELENGTH implies HIGH FREQUENCY