Do Muslims Worship the Kaaba?

No, Muslims worship God in heaven. The Khaba also known asal-Masjid al-Haram  is the house of God on earth and it is the direction of prayer Muslims face when performing the obligatory prayer (Salah).

Bukhari, Volume 6, Book 60, Number 19:

     Narrated Al-Bara:

     We prayed along with the Prophet facing Jerusalem for sixteen or seventeen months.
     Then Allah ordered him to turn his face towards the Qibla (in Mecca):–

     “And from whence-so-ever you start forth (for prayers) turn your face in the direction
     of (the Sacred Mosque of Mecca) Al-Masjid-ul Haram..” (2.149)

The Prophet Muhammad longed to face Mecca in prayer and God has seen his yearning.

Quran [1:144] We have certainly seen the turning of your face, [O Muhammad], toward the heaven, and We will surely turn you to a qiblah with which you will be pleased. So turn your face toward al-Masjid al-Haram. And wherever you [believers] are, turn your faces toward it [in prayer]. Indeed, those who have been given the Scripture well know that it is the truth from their Lord. And Allah is not unaware of what they do.