Is just simply believing 'La-ilaha-illallahu-muhammadarrasulullah'- "There is no God but Allah, and Muhammad is His messenger"- enters one into Islam? Do they have to believe other things?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If a person believes in the Two Testimonies of Faith of Faith: the testimony that there is no god, but Allah and that Muhammad is the Messenger of Allah, and pronounces them, he embraces the religion of Islam by doing so. Knowing that one of the necessities of belief in the Two Testimonies is belief in everything that was revealed about Allah in His Book, and about His Messenger in his Sunnah. It includes: the obligation to believe in Allah, His Angels, His Books, His Messengers, the Last Day, and the predestination (Decree), the good and the bad thereof. Belief in Allah also includes belief in His Best Names and Sublime Attributes.

Belief in His Messenger includes believing in what he conveyed, obeying him in what he commanded, shunning off what he forbade and reprimanded, and not worshiping Allah except with what the Prophet legislated.

Moreover, among the obligatory faith is the belief in what Allah has made compulsory on His servants to do, such as the five prayers, Zakat (almsgiving), fasting, Hajj (pilgrimage), and other apparent Islamic legislations, while accepting and submitting to it.

Allah knows best.