How do I stain my kitchen cabinets blue?

Personally I like the MinWax water based wood stain in Pearl Gray. If you are going to go with a blue make it a light shade and not to over powering unless that is what you want. Here is a link with colors to choose from.

https://www.sherwin-williams.com/homeowners/color/find-and-explore-colors/stain-colors/interior-stains

You would need to sand down to raw wood to stain. Stain needs to absorb into the grain.

you could use a glaze to mimic a stain ... and seal it with a durable poly since it's going to get more 'wear/tear' in a kitchen environment

https://paintcouture.com/glaze-couture/

Lightly sand them sown so paint will stick

Are you sure you want to stain on oak? You will get a ton of grain showing through and it could take numerous coats to get the look you want. If you want a more solid look I woul recommend using paint and diluting it with water so you can control the color. I've not used the colored stains so I don't know how they work or what you are trying to achieve. Color is a big commitment so be sure. Go to some cabinet shops and see what their samples look like. Oak is a tough to work with because of the grain. Birch and maple are closed grains and easier to work with. As a professional I always recommend a neutral color such as dove gray, or basic white or even a green gray. They have more longevity. Good luck.