The most beneficial and most important islamic knowledge to learn is knowing Tawheed. In this short article, I will explain The 3 Aspects of Tawheed.
The first aspect of Tawheed is lordship. It means to single out all of what Allah does and His ownership. Everything we see and hear is caused by Allah alone.
The second aspect of Tawheed is to worship Allah alone without partners. Worshipping other than Allah is shirk, meaning this is a hateful and evil act which will not be accepted as a good deed. This aspect also means that us Muslims must single out our own deeds for the sake of Allah alone (subhanahu wa ta'ala).
The final aspect of Tawheed is the oneness in Allah's names and attributes and to single Him out with His names and attributes. Also, this is to affirm that Allah has affirmed in the Qur'an His own names and attributes, which the Prophet ﷺ also affirmed for Allah without denying, restricting, or innovating them.
Now you know all the aspects of Tawheed. In brief, Tawheed Al-Rububiyyah is to single out all of what Allah does, Tawheed Al-Uluhiyyah is to worship Allah (subhanahu wa ta'ala) alone without partners, and lastly, Tawheed Al-Asma Wa-Sifat is the oneness of Allah's names and attributes.
May Allah bless you, and shukran.