The Messenger of Allah (sallallaahu alaihi wa sallam) said: Islaam is built upon 5;

1. The Shahaadah (testification) that there is none that is truly deserving of worship except Allah, and that Muhammad is the Messenger of Allah
2. The establishment of the (five compulsory) Prayers
3. Paying of Zakah (Obligatory charity paid annually if minimum level of wealth has been reached and maintained for a full Islamic year)
4. Performance of Hajj (Obligatory major pilgirmage (performed once) to the Kabah in Makkah, for those who have the ability)
5. Fasting the month of Ramadhaan

So the Shahaadah: Laa ilaaha illa Allah:

Is the knowledge, belief and adherence of the slave that there is nothing (or no-one) deserving of divinity or worship except Allah Alone, having no partner.

Therefore that which is obligated upon the slave:

Is to purify and sincerely (direct) all (affairs) of the religion to Allah [The Most High], and that the slave’s acts of worship – the apparent and the hidden – are all for (carried out for the sake of) Allah alone, and that he does not associate any partners with Him in any of the affairs of the religion.

This is the foundation of the religion of all of the messengers and their followers as Allah the Most High has said:

وَمَآ أَرۡسَلۡنَا مِن قَبۡلِكَ مِن رَّسُولٍ إِلَّا نُوحِىٓ إِلَيۡهِ أَنَّهُ ۥ لَآ إِلَـٰهَ إِلَّآ أَنَا۟ فَٱعۡبُدُونِ

And We did not send any Messenger before you [O Muhammad (sallal-laahu-alayhi-wasallam)] but We revealed to him (saying): Lâ ilâha illa Ana [none has the right to be worshipped but I (Allâh)], so worship Me (Alone and none else).” [Al-Anbiyaa (25)]

And The Shahaadah that Muhammad is the Messenger of Allah:

That the Slave believes (and holds as creed) that Allah sent Muhammad to all of the humans and jinn, a bringer of glad tidings and a warner, calling them to single out Allah [in worship (Tawheed)] and to obey Him, by affirming the news/information (Allaah has made known to them),  obeying His commands and staying far away from His prohibitions. And that (the person) believes that there is no happiness and no salvation in the worldly life or hereafter, except by way of eemaan (belief) in Allaah and by obeying [the Messenger (sallallaahu alaihi wa sallam)]. And (know) that it is obligatory to put love of him before love of yourself and your children and all of the people.

And (to believe) that Allah aided him with miracles, as an indication of (the truthfulness) of his message and the complete knowledge Allaah gave him and (his) high moral character, and that his religion is comprised of guidance, mercy and truth; worldly and religious benefits.

And the greatest sign is this Great Quraan, due to the truth it contains, the information about (various affairs of the worldly life and the afterlife), commands and prohibitions.

And Allah knows best.

Manhaj As Saalikeen wa Tawdeeh al Fiqh fid deen (pages 5-6). slightly paraphased. Publisher: Daar Ibn Jawziyyah