Through the ten Guru's the word of God, Guru Granth Sahib Ji (the Sikh scriptures which is know the 11th Guru) was revealed. Guru Granth Sahib Ji, or the hymns inside it
Gurbani envoke the true love of God. Without following the Guru's in the form of the hymns given to us by them, one cannot reach God.
The aim of life and the only goal a Sikh should have in mind is to love God, nothing else.
Sikhism has two aspects- 'Miri and Piri'- Miri means having a political side, living in the world and contributing to it, while Piri means having a spiritual side.
This ties into the Sikh ideal of being a "Sant-Sipahi", a Saint-Soldier. For this reason one of the compulsory items for baptised Sikhs (5 Ks) is a small sword. The other four are the hair and turban, comb (cleanliness next to Godliness!),Kara which is an iron bangle and also special shorts which are in practical terms a reminder that you are a Sikh so don't do anything dodgy *ahem* and also they are designed for freedom of movement in a fighting atmosphere.
The spiritual side is simply put following everything written in Gurbani, and reading certain daily prayers and incorporating what they say into your life. Love God, think of him in everything you do, follow the Guru 100%, there are also four sins which are the worst and would require you to be re-baptised into Sikhism if you commited any one of them, they are:
1)Cutting hair
2)Sexual relations outside of marriage
3)Eating meat
4)Taking any intoxicants
One common saying used to describe Sikhism is "Naam japo, kirat karo, vand chako", basically, be spiritual, earn an honest living and share with others.
Sorry if that post was abit all over the place lol, bit busy. Hope it helped