You have to water the "plants" until they grow and thank you. After they disappear, more will come up but you need to make sure you don't let them sit for too long or they'll regress. If that happens and you let either one regress too much/too long, you lose.
As for controls, directional buttons need to be pressed each time you move and the a button is for watering. You go up to the water to refill your watering can, which will have the number of times left before you need to refill up on the screen as a counter.
If you need anymore help just let me know. :)