In the So Sethaputra online dictionary, what is the dot used for below a character?
As Mr. Setheputra mentions in the Preface of his "Modern Thai-English Dictionary," the mark "." is used to avoid misreading. Take for example, the word "แปฺลง" should be read "plang" not "pa-long." Please notice the "pl." Without this mark, you then might read "pa-long," which is wrong.

Likewise, "เหฺลี่ยม" should be read "leam"; "กฺริยา" "kri-ya."
Of course, without the mark, "กฺริยา" may be read "ka-ri-ya," which is wrong. (I don't want to make this more complicated but "ka-ri-ya" is spelled "กิริยา")

w-bpf

Is the "ศรี" in the School's name pronounced "สี" (see) as in "ศรีราชา" ?
Yes, you are right. ศรี = สี = see

The same as the city you mentioned and other words like this.

Interestingly, notice that ศีรษะ is pronounced สี-สะ (see-sa)

There no words starting with "ษ, ซ, ส" together with "รี" and pronounced "see".

BUT, there is สรีระ which is pronounced สะ-รี-ระ = sa-re-ra

How do you speak in past sentences in thai?
Unlike English, Thai words don't change when you want to talk about past events. For example:

"I missed you"

In Thai you would say something like: "perod of time last year I miss you"

muea bee tee laew pom kit teung koon เมื่อปีที่แล้วผมคิดถึงคุณ

muea bee tee laew = period of time last year
bee tee laew = last year

Another way to show a completed action is to add "laew" แล้ว

She has gone already = kow bai laew เขาไปแล้ว

If you want to say you have been already and come back:

pom bai ma laew ผมไปมาแล้ว

Or you have seen a movie already:

pom doo ma laew ผมดูมาแล้ว

I hope this helps a little.

Listening to the sounds for the letters, I don't hear the Rs for Gor, Kor, and Khor. Are they silent?
It is very difficult writing Thai sounds with Roman letters. The letter "r" is a good example. I am told that English and American don't pronounce the "r" in the same way! My teacher is native English. Maybe you are from America?

anyway, I suggest you only use the Roman letters as a guide but concentrate on listening to the sounds. Writing first is OK as long as you learn the sounds of each letter as you go along. Maybe as you write the letters you should say the sounds aloud.

What is an easy way for me to learn the Thai alphabet?
Try downloading our Thai Alpabet Trainer. You will be able to repeat after me saying the alphabet.

http://www.learningthai.com/downloads.html

Do adults really spell Thai words by saying "gor gai" etc?
You don't have to worry. "gor gai" is OK, and you wouldn't sound like a kid by doing so. However, you can also say just "gor." for example, to spell the word "กิน" (eat), you can say either "gor i nor" or "gor gai - sa ra i - nor nuu."

gor = gor gai = ก
i = the vowel อิ
nor = nor nuu = น
sa ra means vowel

- w-bpf

Do you have a guide to write Thai letters in English?
This is very difficult to do as no-one in Thailand can agree. But we have a guide on our web site that is used by many people:

http://www.learningthai.com/romanization.html