Kaaba is the Qibla i.e. the direction Muslims face during their prayers. It is important to note that though Muslims face the Kaaba during prayers, they do not worship the Kaaba. Muslims worship and bow to none but Allah. It is mentioned in Qur'an: ?We see the turning of thy face (for guidance) to the heavens: now shall We turn thee to a Qiblah that shall please thee. Turn then thy face in the direction of the Sacred Mosque: wherever ye are, turn your faces in that direction.? For instance, if Muslims want to offer Salaah (Prayer), it is possible that some may wish to face north, while some may wish to face south. In order to unite Muslims in their worship of the One True God, Muslims, wherever they may be, are asked to face in only one direction i.e. towards the Kaaba. If some Muslims live towards the west of the Kaaba they face the east. Similarly if they live towards the east of the Kaaba they face the west.
Kaabah was built by prophet Ibrahim(A.S) on Allah's orders.. it is a place where all Muslims gather around Hajj on Islamic month of Zilhajj . and they perform Hajj which consists of five days.. Kaaba is present in Masjid E Haram .. Kaaba is sort of the House of Allah.. so Muslims all around the world bow their heads towards Kaaba(towards Allah) when offering prayers which they offer five times a day.. Muslims also go to Kaaba throughout the year for Ummrah .. and they visit Masjid e Nabwi in Madinah as well where Holy Prophet Muhammad (S.A.A.W) was buried and is one of the most beautiful Masjid in the entire world. btw Kaaba is just a plain building over which there is a black cloth which has ayat written on it with gold .. and it is a holy place for Musims throughout the world.