kudasai

I hear the word kudasai at the end of a sentence. i believe it is a modifier, but how and when is it used?

I don't know why you thought it was a "modifier" (like an adjective or an adverb?), but it is combined with the "te-form" of a verb to make a sentence for request.

Take a verb "kuru/kimasu," meaning "to come (over here)."
You take the te-form of the verb, which is "kite," and combine with "kudasai" to say, for example,
- Kochira ni kite kudasai. (Please come over here.)

"miru/mimasu" (to look at, to watch, to see): te-form is "mite"
- Howaito boodo wo mite kudasai. (Please look at the whiteboard.)

"kiku/kikimasu" (to listen/to ask)
- Watashi no hanashi wo kiite kudasai. (Please listen to me.)

by a modifier i was thinking it came at the end sometimes.
i am a beginner at this. sorry. i then would ask about the te form
i have a lot to learn..thanks AK

If you pick up a grammar book, this "te form" will come up probably quite early in the textbook, as it is a very useful form to learn, as this "te form" of verbs are combined together with other words to express different meanings :)

For making a request:
- Te-form + kudasai, as in my earlier post

For asking permission:
- Te-form + mo ii desu ka. (Is it OK to do this/that, so "may I do something?)
Example, with the verb "hairu/hairimasu," the te-form is "haitte."
- Haitte mo ii desu ka. (May I come in?)

Expressing actions you do one after another: you can list a few things you do in a series.
Example: with verbs "okiru/okimasu" = to get up (te-form: okite), "kiku/kikimasu" = to listen to (te-form: kiite), "iku/ikimasu" = to go (te-form: itte).
- Mainichi 7-ji ni okite, rajio wo kiite, gakko ni ikimasu. (Everyday I get up at 7, listen to the radio, and go to school.)

etc., etc. Enjoy learning!

thank you for the explanation , I'll be working on it.

There are two ways of expression. The latter here is good to know how to say at a restaurant or at a store.

As said "...te kudasai"= "I request you to do .." or "do..., please and written in Hiragana　”ください”. However, there are exceptions when said more politely. For instance, "okiki kudasai" which is more polite than "kii te kudasai"

And "noun +(を, wo)＋ kudasai"="please give me noun" or "noun, please", which comes from "kure"= give me” . In this instance it is written in Kanji "下さい”. (を, wo) is often unused.
I.e. When you go shopping, you say, An apple, please=ringo (wo) kudasai. Or at a restaurant, ramen (wo) kudasai,
How is written is confusing even for Japanese so don't worry . Both are polite with respect.

As far as when to use it, the others are correct with the use of kudasai. There is also onegai/onegaishimasu that are also used as a sort of "please", but in different situations. The way I separate when to use each one is "kudasai" is more of a command or you expect , and "onegai" is more of a request.

This is the best explanation I've found for choosing between the two:
The main difference is that onegaishimasu assume some action/favor by the other person. It's also a meaning of "I trust this to you".

ください Kudasai (and the more familiar chodai ちょうだい) it's used when you did a request you are entitled to do. You want something or you want someone of same/lower status to do something for you (verb-te+kudasai).

"Kudasai" means "please".
"Noun(A) + wo + kudasai" means "I want A".
you can use this phrase everywhere.

wow this is a very interesting thread... does that mean kudasai can always be use after any word that ends with "te", and is it mostly/only used after "te"?

If we use "Kudasai" with verb + "te", the verb will be changed to "instruction form". It is difficult part of Japanese language rule.
The below is incorrect Japanease, but you can use verb + "shite" + "kudasai". Japanese people can understand what you want to say.