If you have a good GPU, you should be able to run a model without issue. The big ones are technically usable with tweaking but so slow enough to be useless on normal hardware. A small model may be 4-8 gb, but a larger one could be 100+gb. You don’t need the training data(if its even public) to run them, only if your building or retraining the model. There’s a crap ton of different software to run AI on.
To get started assuming you got a beefy PC, you need a model and software to interact with it. I started with mistral7b and textGenWebUi and been trying out different software and models. Text gen has the basics to load and chat to a model and is a good starting point.
For Images, you can choose models at based on what the sample images look like, they tend to be specialized for certain styles or content. You can add LORAs to further change how the output looks(think specific characters or poses). It’s very much trial and error getting good images.
There’s more models and software out their than I can keep track of, so if something is crap you should be able to find an alternative. Youtube guides are you friend.