Estar is kind of an irregular verb in Spanish, it doesn't have the same endings as a regular ar verb. For the yo (I) form it's estoy . For the tu form (you informal) its estas with an accent on the a. For the ud, el, ella form (you formal, he, she) it is esta with an accent on the a. For the nosotros form (we) it is estamos with no accent. For the vosotros form (you all informal) it is estais with an accent on the a. for the uds, ellos, ellas form (you all formal, them(masculine), them (feminine) ) it is estan with an accent on the a. All forms have accents on the a except estoy and estamos