Sikhism is a spiritual path based on love and sacrifice. There is nothing else. It's a very simple straight-forward path.
When you take a look at the history of Sikhism going back 300-500 years, you'll see they had 10 Gurus. All preached on universal love and sacrifice for the benefit of others. They sacrificed themselves for other religions as well.
The 10th Guru made their holy book, which is a collection of spiritual poetry of beings who had attained the highest, these were writings of beings outside of the Sikh Gurus as well. Beings with different religious backgrounds. Truth is the Truth, Light is the Light regardless of color, creed or religion. There is only 1 Truth.
Sikhism really does not have a set of requirements to be a Sikh, it's teaching are universal because it is all about universal love and connecting with God, you'll see that in the scriptures. Anyone can be a Sikh(open-minded learner), the gurus even taught to study other scriptures and teachings to see what you could get from them.
The Tenth Guru created a discipline and mandate for those who wished to be Khalsa(The Purest of the Pure, Image of God) this was so others could know if they ever saw these Khalsa people that they'd be images of God and could be helped by them(it kind of backfired lots of fake ones with outside robes etc. but empty inside).
The common theme you will find is universal love and sacrifice in their scriptures, it is spiritual poetry with such a steady rhythm that it can be listened to day and night. This is a path of steadiness, so their scriptures are written with such attention to vibration and sound and meaning to create a steady energy flow that never gets old. It is always new, always refreshing.
For their spiritual path they use japa of the mantra Vaheguru, Vahe(Wow) Gu(Darkness) Ru(light)
Vahe-Guru Vahe-Guru Vahe-Guru is chanted over and over and over to clean the mind from the veil of darkness that is keeping it from realizing itself.
They recite 5 main prayers and listen to Kirtan(Singing of Scriptures) throughout the day, they are always blissed out. They are enveloped in love for their Creator day and night. They have no other support.
Vahe-Guru describes the journey from Darkness to the Light, all you can say is Vahe(Wow) when you have that experience.
They meditate upon the subtle unstruck sound and the whole holy book is basically praise of this subtle sound which can lead one back to their true home, it can lead one to the highest. Different names for this sound from different traditions such as Amen, Aum, Ong. Sikhs connect with this sound for their path to self-realization.
They refer to this sound as Gods' voice and its' calling them home, they listen to it with much 💖, some just call it energy. But to them it is much more, the thing is all this energy has intelligence and it is Gods' voice/consciousness itself in the view of the true Sikhs. In the view of Sikhs from this sound came the 5 elements and the creation, this sound came from the creator so it makes sense that it can lead one back.The whole holy book is praise of this sound. The japa and purpose of mantra is to get closer and deeper to this unstruck sound which is resounding through the whole universe and creating everything.
I know this path because I walk it. I am a Sikh 🙏
There is deeper spiritual stuff but I feel this is a nice summary