Mixed orthography is very popular today, and slowly becomes de-facto standard in Israel (although I personally think it's a little bit controversal.) The idea is to show Hebrew words written with exactly the same letters, regardless of using vocalization or not. Actually, this is the way many Israelis would "intuitively" vocalize the Hebrew words: first write it the usualy way like they are written in כתיב מלא and then add some minimalistic vocalization.

Consider the following words:

Hebrew, what a language! In Hebrew, she is hee, he is hoo, and who is mee...

Now, how would you read this word?

הִוא

That's a standard Hebrew word הוא (meaning "he"), but it's vocalized like the word היא (which means "she".) You can find it in the biblical texts all over the place.

כֹּל - כָּל - כֻּלּוֹ

Why this strange orthography? Why the word keeps changing the vowels in its every transformation?

Why do we write this word without Vav in most cases? Why in Ktiv Maleh we write כל אחד and not כול אחד? And if we write it without Vav, why the Vav might appear in the phrase זה הכול? And why even then it's considered "optional" and not mandatory?

Kamatz Katan (the Little Kamatz, read as "O" in modern Hebrew) is one of the first confusions every Hebrew student is facing. Why, for God's sake, it's the same sign as Kamatz Gadol (the Big Kamatz, read as "A")? How is the reader supposed to distinguish between them? Can I just learn all the "exceptions" with Kamatz Katan?

Usually diacritic marks are written under/above/inside the letter after which they are pronounced. (There are some exceptions, however.)

There are 4 categories of vowels in Hebrew: