If you are cool just using the command line, ollama is great and easy to use.

Otherwise, you could download LMStudio app on Mac, then download a model using the search feature, then you can start chatting. Models from TheBloke are good. You will probably need to try a few models (GGML format most likely). Mistral 7B or llama2 7B is a good starting place IMO.

I bought a fancy 4090 rig and returned it but mostly because I want a more powerful rig