Practising of Islam started when Muhammed (pbuh) left.
He introduced what was islam fully and told that everyone should practise because the old religion were outofdate.

E.G. if you have software it gets old and new one comes out and you need to up grade.

Likewise Islam is the last true religion and it alwalys existed.

Holy books before Quran were for people who understod them then it got much simpler to Quran and it contains all the guidence for mankind.

Example. Operating system DOS came out which was hard but people who understood it knew how to use it like wise the holy books before Quran. Then came out Windows 95 etc which were easy to use and more people understood it.

Every prophet form Adam(as)>>>>>to>>>>Muhammad(pbuh) had same message that there is only one god that is Allah and people who will worship him will be reward in here after.

Five pillars are the key things for muslim they should do in their life. Its the basic for being a good muslim. They are other which will make you the righeoust of all if you follow all the sunah of Prophets(pbuh) and stay away form evils.

Mahammat Ghandi indian freedom fighter said "

DONOT Listen to EVIL
DONOT Hear EVIL
DONOT Think EVIL.

And prophets has been alwalys practising them. Its a mystery like in the Battle of Badra angels came to help muslim army aginst kufar.

Prophets used to not eat for days and days and one companion of Prophet did similar but he was ill and Prophet said to that companion that you dont know but i angels by the command of Allah comes and feed me.