First up, we're diving into the most commonly used low class consonants.
In Thai, consonants are grouped into three categories: low class, mid class, and high class. The class of a consonant plays a big role in determining the tone of a Thai syllable.

Vowels can be positioned to the left, right, top, or bottom of the consonant. Above we have an example shows both: long vowel and short vowel.
This character, ๏, is simply a placeholder for a consonant, because in Thai, vowels always accompany atleast a consonant.

Putting all together we notice that a typical syllable is:
With C as a consonant and V as a vowel.