We Muslims worships our Lord Allah SWT in different ways and one of these ways of worshiping Allah is Sujud (Sajdah). In Sujud (Sajdah) we go into prostration position in direction of Kaaba and glorify our creator Allah SWT.
In Sujud forehead, nose, both hands and knees of a person must touch the ground otherwise it not gets completed. Sujud is a must part of Salah (Namaz) that we perform five times a day. after every rakat of Salah two Sujud are done during which we read Subhana Rabbi Al-A`la at least 3 times.
We can also do Sujud when we are not offering Salah and we can do dua during this. Rasool Allah SAW also used to do Sajdah whenever he heard a good news. there are also some specific verses of Quran when a person reads them the Sujud becomes necessary for him. if while offering Salah we forget something then at the end of Salah Sujud as-Sahw is done.
Allah SWT really loves those people who do Sujud in-front of him. According to one Hadith Allah's most favourite worship position that a Momin do is Sujud. There are also many verses in the Quran About it. Quran says "Indeed, those who are near your Lord are not prevented by arrogance from His worship, and they exalt Him, and to Him they do Sujud."
It must also be kept in mind that Sajdah is only for Allah and doing it to someone else except Allah will be act of Shirk. Now a days we see many people doing Sujud to graves or to big scholars. Remember it is completely Haram and Shirk.