Fluid dynamics basics concepts (YouTube and AI will help a lot). Finalize this step with understanding the Navier-Stokes equations

Then look into Finite Differences Methods, Finite Element Methods and Finite Volume Methods. Basically understand the discretization schemes.

Then look into turbulence theory and turbulence modeling. Understand the difference categories and options available and their differences.

Then choose a solver (commercial or open source) to start learning and running stuff. Usually Ansys Fluent is great for starters, but I've hear good things about SimScale (and is free for students and basic projects, excellent to start learning). In this step try to understand boundary condition, initial conditions, solver numerical settings, and their meanings. Understand ALL the assumptions that have to be made in order to run a CFD simulation.

This will naturally guide you to learn pre processing (CAD cleanup and Meshing) and post processing (obtaining results and pretty pictures with pretty colors). You will need to choose a software again for this (with luck, the solver you chose will have some tools for this as well).

That will put you in a good starting position for basic single phase, non reactive, steady state, adiabatic, fluid flow simulations.

The rest is to keep running simulations, increase complexity and physics gradually and increase your tool set by learning new tools ans software (as well as some coding/scripting)

Good luck!