The most basic of all Thai letters is ก. In Thai, the official name of each letter has both a sound component and a word component. Similar to how you might say "A as in Apple, B as in Boy", a Thai person would call this letter "Gaw as in Gai", or simply "Gaw Gai".
Here, the word "Gai" means Chicken. You can see that the letter even looks like a chicken. The letter's sound is usually transcribed into English as the letter G, but it really makes a sound somewhere between a G and a K.
In the Thai language, each sentence is made up of words, and each word is composed of one or more syllables. The most basic syllable is composed of an initial consonant sound, a vowel sound, and finally either a dead-ending or a live-ending. The letter ก at the beginning of a syllable produces an initial G/K consonant sound, but at the end of a syllable, it instead produces a "K" dead ending, or "K-Stop".
For example, consider the word กก. It has an implicit short "oh" vowel sound between the two consonants. It might be transliterated as "gohk". But the final "K" is not really a "K", it is a "K-Stop". This means you don't fully pronounce the "K". Imagine your mouth begins to form the final "K" just as the word ends, without actually speaking the "K". This is how all dead-endings work in Thai.Click to listen: "กก"