Your task in the game is to manage the transport of peolple (and cargo, if you choose this option in your initial settings). You simply set routs/trails/airways between cities, choose a vehicle from several options and set ticket prices. After that you can go for a tea or lunch, waiting for money to grow so you can set another road, buy another bus or plane, charge for more tickets and so on. After a while it gets so boring that you just quit and never play again.
But seriously, the game is too simple. All paths for vehicles are premade, you can just select cities to conect. There is no track building, no tunnel building, no bridges, just a simple dot to dot connection. After purchasing a vehicle, you can set ticket prices and add some costly upgrades to increase passenger comfort. Then, unless you really enjoy doing it manually, you just leave the repairs to the manager. And that's all there is to it.
The game is fairly easy to learn but not intuitive. It has some annoying things, like when your vehicle starts going from town to town before you set your prices, so it's empty for a couple of rounds, burning up your cash. However, after all this grumbling, I still don't think it's a bad game, especially for someone just getting started with this type of game. It's just that I have been playing OpenTTD for years and this level of complexity is boring for me now.