First off, you'll unlock the Slot Cars mode. This just uses the pedal Toy-Con to control the speed of a car on a fixed track - think Scalextric but without the brand name.
It's a quick, no-frills mode which gives you a nice break once you've finished your first build of the pack, but not much else. Don't expect to be coming back to this mode that often.
The real meat of the game is in its Adventure mode. Here, you're given a remarkably large open-world to explore in your various vehicles, full of objectives to complete and various secrets to uncover as you go.
You can switch seamlessly between vehicles by swapping out the key Toy-Con between each vehicle Toy-Con, allowing you to quickly switch up the action when you get bored of a certain mode of transport.
Each vehicle has its own benefits, too. The Car can carry objects on the roof and has a bunch of tools at its disposal which are better left to be discovered by yourself. It's also the only vehicle which can refuel, which you'll need to do fairly regularly as your fuel gauge is prone to wiping out quickly.
The Submarine has the obvious benefit of being able to travel underwater and can also fire out a sucker to attach onto objects and yank them around - handy for removing steel boxes surrounding sunken treasure.
And finally, the Plane flies super-fast and can fire missiles willy-nilly, both freely and by locking on to a target. However, it consumes fuel like it's going out of fashion, so you don't get to play with it for very long before having to switch back to the Car.
You need to use each of the vehicles at your disposal to blow stuff up, help out the inhabitants of the world, and generally muck about and have fun.
And it really is great fun. There's plenty to do, even if what you actually end up doing is a big fat load of nothing, and just drive aimlessly around causing chaos. There's a lot of "make-your-own-fun" gameplay on offer, but not because there's a lack of content.
If you want something a lot more structured, there's also two-player Battle modes with the Car Toy-Con, and a Rally mode which gives you set races to take part in, utilising every Vehicle Toy-Con at your disposal.