All and Some

كُلٌّmeans "each" or "every" when followed by an indefinite singular noun:

.في الْمُؤْتَمَرِ تَكَلَّمَ كُلُّ رَئيسٍ
Each president spoke at the conference.

When followed by a definite noun, كُلٌّ means "all":

حَضَرَ كُلُّ الرُؤَساءِ الْمؤْتَمَرَ.
All the presidents attended the conference.

The noun that follows كُلٌّ, definite or indefinite, is in the genitive case. A pronoun suffix may be attached to كُلٌّ to mean " all of them, all of it, all of us," etc.:

حَضَرَ الرُؤَساءُ كُلُّهُمْ
The presidents came, all of them.

قَرَأْتُ الْكِتابَ كُلَّهُ
I read the book, all of it.

ذَهَبْنا كُلُّنا إلى الْمُحاضَرَةِ
We all went to the lecture.

أَكَلْنا الدَّجاجَةَ كُلَّها
We ate all of the chicken.

بَعْضٌ means "some" and is followed by a definite noun in the genitive case;

قَرَأْتُ بَعْضَ الْكُتُبِ
I read some of the books.

بَعْضُ الرُّؤَساءِ حَضَروا إلى الْمُؤْتَمَرِ
Some presidents attended the conference.

As in the case of كُلٌّ , a pronoun suffix may be attached to بَعْضٌ to mean "some of."

ذَهَبَ بَعْضُنا إلى الْمُؤْتَمَرِ
Some of us went to the conference.

أَعْرِفُ بَعْضَهُمْ
I know some of them.