• First Steps in Ham Radio - a series of articles intended to help you get started.
• ARRL Technical Information Service - numerous links and articles on a variety of technical topics

The Wikipedia’s entry on Waves has many links to all aspects of waves: frequency, phase, wavelength, etc.  Links to tutorials and simulations are provided at the end (bottom) of the entry.  You will find a great deal of information about the electromagnetic and radio spectrum in the Wikipedia, as well.

Saying the Same Thing -- Frequency & Wavelength

The formula λ = c / f also illustrates two important relationships between frequency and wavelength. First, as frequency increases, wavelength decreases and vice versa. This is true because the wave is moving at a constant velocity. A higher frequency wave takes less time and so moves less far during the time it takes to complete one cycle. Waves at very high frequencies have very short wavelengths--such as microwaves that have frequencies above 1 GHz. The so-called "long waves" are those with frequencies below 1 MHz, such as those used by AM broadcast stations.

Second, if you know the frequency of a radio wave, you automatically know its wavelength, too! This means that you can use the most convenient way of referring to a wave and still be accurate. For this reason, it's very common for the amateur bands to be referred to by wavelength. For example, it's not uncommon to hear a ham say something like, "I'll call you on 2 meters. Let's try 146.52 MHz." The frequency band is referred to as "2 meters" because the radio waves are all approximately that long. The exact frequency then tells the hams precisely where to tune.

• Lesson 2 from this collection of animated tutorials on waves illustrates the relationship between frequency and wavelength.

• Repeaters- What They Are And How To Use Them – An ARRL Technical Information Service tutorial
  
• Repeaters – The general ARRL TIS page on Repeaters

• Untangling the Decibel Dilemma
• A Helpful Discussion About Converting Units
• Tutorial on Scientific Notation
• The Metric System
• Tutorials on Math for ARRL On-Line Courses and License Exams