[aliasaria]

You can chat with the models directly in the same way you can chat with GPT 3.5.

Many of the opensource tools that run these models let you also edit the system prompt, which lets you tweak their personality.

The more advanced tools let you train them, but most of the time, people are downloading pre-existing models and using them directly.

If you are training models, it depends what you are doing. Finetuning an existing pre-trained model requires lots of examples but you can often do a lot with, say, 1000 examples in a dataset.

If you are training a large model completely from scratch, then, yes, you need tons of data and very few people are doing that on their local machines.