For starters [to rapidly get background to understand the state of computational chemistry], the core of this course in Quantum Chemistry is extremely helpful. It is comprised of about 120 very-well produced videos [typically about 6 - 9 minutes long, although some are slightly longer/shorter] ... these bite-sized videos are organized into 10 chapters, although you might find that you want to refresh your understanding of terms or concepts in related applied areas like Surface Science or a more foundational area like Quantum Chemistry or, more generally, in Physical Chemistry.
For starters [to rapidly get background to understand the state of computational chemistry], the core of this course in Quantum Chemistry is extremely helpful. It is comprised of about 120 very-well produced videos [typically about 6 - 9 minutes long, although some are slightly longer/shorter] ... these bite-sized videos are organized into 10 chapters, although you might find that you want to refresh your understanding of terms or concepts in related applied areas like Surface Science or a more foundational area like Quantum Chemistry or, more generally, in Physical Chemistry.
Another source of background would be a course such as 8.04 Quantum Physics I, which the first course in the undergraduate Quantum Physics sequence, followed by [8.05 Quantum Physics II](https://ocw.mit.edu/courses/8-05-quantum-physics-ii-fall-2013/) and 8.06 Quantum Physics III.
There's not really any substitute for doing lots of reading and maybe sketching out math on a scratchpad. There are excellent texts available on Perlego such as Quantum Chemistry or Computational Quantum Chemistry or Density Functional Theory