I recommend you try Singorama for learning Singing.
Their lesson on Major And Minor keys will tell you all about major and minor keys and scales, as well as a system called Solfege. You will be building on things like time signatures, key signatures and rhythm.
You will understand the difference between major and minor keys and scales and to be able to hear the differences as well. Plus you will master the Solfege system that will help you in your singing training now and in the future.
What Are Solfege
In music, solfege (pronounced /'soʊlfɛʒ/, also called solmization /sɒlmɨˈzeɪʃən/) is a pedagogical technique for the teaching of sight-singing in which each note of the score is sung to a special syllable, called a "solfege syllable" (or "sol-fa syllable"). The seven syllables normally used for this practice in English-speaking countries are: Do, Re, Mi, Fa, So, La, and Ti.
Traditionally, solfege is taught in a series of exercises of gradually increasing difficulty, each of which is also known as a "solfege". By extension, the word "solfege" may be used of an instrumental étude.
There are two main types of solfege:
Fixed Do, in which each syllable corresponds to a note-name. This is analogous to the Romance system naming pitches after the solfege syllables, and is used in Romance and Slavic countries, among others.
Movable Do, or Solfa in which each syllable corresponds to a scale degree. This is analogous to the Guidonian practice of giving each degree of the hexachord a solfege name, and is mostly used in Anglo-Saxon and Germanic countries.