Zaid Alsalami, Shaykh Dr Zaid Alsalami is an Iraqi born scholar, raised in Australia. He obtained a BA from Al-Mustafa University, Qom, and an MA from the Islamic College in London. He also obtained a PhD from... Answered 6 months ago

Bismihi ta'ala

There are two ways of performing a ghusl:

Tarteebi (sequential): This method means you must wash in a certain order, or else it will be invalid. The sequence is washing your head and neck, then your right side, then your left side, overlapping each side to make sure that particular section was washed completely. 

Please watch this tutorial for better understanding:

Irtimasi (immersive): This is when you submerge your whole body underwater, and then make your intention for the ghusl you are performing. In this case, as you have immersed your complete body underwater, you do not need to observe any sequence of washing parts of your body, like the above ghusl.

Also, you must refer to your Marja' taqleed for these details, and what their specific fatwas may be.

And Allah knows best.