In quantum Mechanics, Observable are the linear operators defined in Hilbert space representing the state space of Quantum states.

To know about the operators, I would recommend you to see the page No.171 of Zettili Quantum Mechanics  or 188 page of Quantum Mechanics PDF.

Zettili Quantum Mechanics PDF link below:

http://www.mmmut.ac.in/News_content/02110tpnews_11232020.pdf

I hope this answer helps. All the very best for your future endeavors!