"stop" in Japanese is "やめて" and its pronounced as "yamete". its used when you are ordering a person to stop doing something like when someone is doing something annoying and you want them to stop it. If you say "yamete" it would actually be kind of rude, but if you say "やめてください" (yamete kudasai), which means "please stop it" will be nicer.
If you want to tell someone to stop moving while the person is walking or driving a car, you can say "止まってください"(tomatte kudasai), but thats the nice way to say it. If it is and urgency, then you can say "止まれ"(tomare!).
Actully you are right, "i understand" is similar to"わかりません"(wakarimasen). "i understand" is actually "わかります", which is pronounced "wakarimasu"
"簡単" or "kantan" means "simple". it is the opposite of "複雑"(fukuzatsu)
sentence: 卵の作り方は、とても簡単だ。(tamago no tsukurikata wa, totemo kantan da). It means, "the way to cook (作り方/ tsukurikata) eggs (卵/ tamago) is very simple (簡単/ kantan).- the way to cook eggs is very simple.
"全て" or "subete" means "everything".
sentence: 全てを書いてください。(subete wo kaite kudasai). It means "please (ください/ kudasai) write (書いて/ kaite) everything (全て/ subete).- please write everything.
As you can tell, the Japanese grammar is very different from the English grammar. In a book for learning Japanese i actually read that for you to learn how to speak Japanese, you have to learn how to think backwards the way yoda from star wars talks.
I hope this helped, if you have any more Japanese questions, i'd be happy to answer them, you can e-mail me if you want.
good luck.