Music Theory
Music theory.net: Steps and Accidentals
Provides an explanation of half steps, whole steps, flats, and sharps. Illustrated examples accompany these definitions.
Music Theory
Music theory.net: The Minor Scales
Listen and learn with this explanation of minor scales. Each description of harmonic, melodic, and minor scales provides an illustrated example, and audio clips.
OpenStax
Open Stax: Catherine Schmidt Jones: Half Steps and Whole Steps
Take a look at the two intervals of the half step and whole step and how they make up the chromatic and whole tone scales. This page includes a couple of self checking problems to test your knowledge.
Other
Music Theory First Aid for Struggling Students
This site provides music theory information on such topics as rhythm, intervals, scales, chords, etc. Also, there is a fine section which describes the basic concepts of form and structure.
Music Theory
Music theory.net
An online beginning music theory and ear training site. This site is for students to use at home to reinforce what they learn in class.
Other
Teoria: Key Signatures
This site from Teoria's Books offers a short, easy to read article on Key Signatures. An interactive keyboard makes the learning more fun.