When a model has open weights, it means, in simple terms, that the values it learned are available to download. This can make it possible to run the model yourself and customise how it is used.
It does not always mean all the training data is open, or that the model can be used without any restrictions. Its licence explains the conditions. Different models can have different rules, especially when they are part of a product or service.
Google, for example, describes Gemma as a family of open models and refers to specific terms of use. The model’s own information page is therefore a good starting point when you want to go further.
For someone who simply wants to learn, the first step is understanding the possibilities. You can try, compare and build small experiments of your own. Then look at the terms before an experiment becomes something you share or sell.
Source: https://ai.google.dev/gemma/docs