Perhaps you should give the campaign a try. It tends to be a great way to easy players into the game. Each mission has a very specific goal, so you can learn how to properly identify a goal (colonize a system, invade a planet, establish a trade route, take over a race with cultural starbases, ect ect) and work towards it.

In sandbox mode, all the options can quickly overwhelm the new player

I also suggest relearching some weapons techs and building some attack shis in the Ship Designer!

Hope these suggestions help!