Rule 1: 1. Forming the imperative
Take the second-person jussive and remove its prefix تَـ: تَكْتُبْ gives كْتُبْ. The result begins with a vowelless letter, which no Arabic word may do, so a hamzat al-waṣl is prefixed to carry a vowel: اُكْتُبْ write! Like the alif of the article, this hamza is heard only at the start of speech; after a vowel the voice runs straight on to the sukūn letter: وَاكْتُبْ wa-ktub.
اُكْتُبْ دَرْسَكَ يَا وَلَدُ.
uktub darsaka yā waladu
Write your lesson, boy.
اُدْخُلُوا الْبَيْتَ وَاجْلِسُوا.
udkhulu l-bayta wa-jlisū
Enter the house and sit down.
After وَ the hamza of اجْلِسُوا is not pronounced.
اِفْتَحِي النَّافِذَةَ يَا أُخْتِي.
iftaḥi n-nāfidhata yā ukhtī
Open the window, my sister.
اِحْمِلْ هٰذَا الصُّنْدُوقَ إِلَى الْمَطْبَخِ.
iḥmil hādha ṣ-ṣundūqa ila l-maṭbakhi
Carry this box to the kitchen.
اِغْسِلِ الصُّحُونَ بَعْدَ الْعَشَاءِ.
ighsili ṣ-ṣuḥūna baʿda l-ʿashāʾi
Wash the plates after supper.
The final sukūn of اِغْسِلْ becomes kasra before the hamzat al-waṣl of the article.