What are the requirements to join together in Islam?

Nothing particular. It is better for a person who intends to embrace Islam to study the holy Quir'an and try to understand it properly. He must think twice to accept Islam and ensure that he is convinced that he is making the right decision. He should also bear in mind that Islam is a religion, a guidance from his creator- Almighty Allah. Many of the Muslims don't follow many teachings of islam. So don't e discouraged if you find some Muslims telling lies, being cruel, deceiving others. Islam teaches love for all.