Glad you liked it @schmudde!
If you install the extension you will get a new upload button in your jupyter lab/notebook.
Then, whenever you decide to upload a snapshot you click that button (you can name the snapshot and add a description too).
If you want to version your machine learning experiment runs inside of a versioned notebook (a lot of versioning I know), then those snapshots can be generated automatically whenever you run a cell with neptune.create_experiment() in it.
You can see an example of model training in notebook here.