What is the ruling of shaving the head of a newborn baby? I find that some of our people would shave the whole head while others didn’t even do so. Hope for an explanation.
Alhamdulillah, praise and gratitude to Allah SWT for the countless blessings he blesses us all. Praise and salutation to our beloved Prophet Muhammad PBUH, his family, companions and all those who follow his footsteps until the Last Day.
Every baby who is born regardless of whether it is a boy or a girl, it is sunnah to perform aqiqah and shave their hair completely. This is based on a hadith narrated from Samarah bin Jundub RA, where Rasullullah PBUH said:
كُلُّ غُلاَمٍ مُرْتَهَنٌ بِعَقِيقَتِهِ ، تُذْبَحُ عَنْهُ يَوْمَ السَّابِعِ ، وَيُحْلَقُ رَأْسُهُ ، وَيُسَمَّى
“A boy is in pledge for his Aqiqah, Sacrifice is made for him on the seventh day, his head is shaved and he is given name.” 
It is also sunnah to weigh the hair that has been shaved and donate the equivalent weight in gold or silver to the people in need. Rasullullah PBUH instructed his daughter, Saidatina Fatimah R.anha:
زِنِي شَعْرَ الْحُسَيْنِ وَتَصَدَّقِي بِوَزْنِهِ فِضَّةً، وَأَعْطِي الْقَابِلَةَ رِجْلَ الْعَقِيقَةِ
“Weight the hair of Hussein and donate the equivalent weight of silver and then give the leg of the aqiqah animal’s leg to the midwife.” 
Imam al-Nawawi stated in al-Majmu’: It is sunnah to shave the hair of a newborn baby on the seventh day. Our madhhab stated that it is also sunnah to give in charity the equivalent weight in gold of the weight of the baby’s hair. If one isn’t financially capable, then it is sunnah to donate with the equivalent weight in silver. This applies to both male and female babies.
We also advise not to shave the baby’s hair in certain patterns for it is also known as qaza’ and it is prohibited by syarak. From Abdullah bin Dinar RA:
أَنَّ رَسُولَ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ نَهَى عَنِ القَزَعِ
“The Messenger of Allah (ﷺ) forbade qaza’.” 
And it is also sunnah to slather saffron on the baby, Khaluq (a type of perfume stronger than saffron) or other perfumes to replace the Jahiliyyah tradition who slather the head of the baby with the blood from the aqiqah.
This is in accordance with a hadith narrated from Aisyah R.Anha, where she said: During the time of Jahiliyyah (when slaughtering aqiqah) they dip cotton into the blood of aqiqah animal and slather it on the head of the newborn baby (after the head is shaved). Then (after the arrival of Islam) the Prophet PBUH instructed:
اجْعَلُوا مَكَانَ الدَّمِ خَلُوقًا
Make (replace) the slathering of blood with Khaluq (a type of fragrance or perfume from saffron and other fragrances, its color is a mix of red and white). 
 Hadis Narrated by Hakim (4828) and al-Baihaqi (19776). Ibn Hajar al-Asqalani in al-Talkhis al-Habir (4/1500), and Imam al-Syaukani in Nail al-Autar (5/230) stated that this hadith is narrated through mursal.