There is a special symbol " อ์​ " which is used to make the consonant it is above silent. It is mainly used in foreign words and it helps to keep the original spelling.

For example: "John" is " จอห์น​ ".

Sometimes you will see an English word without this cancellation symbol.

For example: "golf" was written " กอล์ฟ​ " and also " กอลฟ​ "

Sometimes the last two letters are silent even though only one has the cancellation symbol:

If the cancellation symbol is placed over a consonant with a superscript or subscript vowel, then both are silent. You will see this more often with " ธิ​ " and " ธุ​ ".

Sometimes the final cosonant is silent even though there is no cancellation symbol. This letter is usually " ร ".

The cancellation symbol is usually only used at the end of words. However, there are some words where a letter in the middle is silent and it isn't marked. These are often " ร " but not always.

Sometimes there is a final consonant where only the superscript or subscript vowel is silent. These are usually " ตุ​ " and " ติ​ ", but also " ดิ​ ", " ฎิ​ " and " มิ​ "