Microsoft Harvest moon/Pokemon Rip-Off is kind of frustrating, though meant for children, it's very hard to understand.
So basically you're given few tools to manage your garden, A Shovel, which is the most important tool, since you'll need it for whacking "Bad Guys", putting holes for growing plants quickly, and digging ponds. The second tool is a Watering Can, which can make certain Pinatas happy, and of course, can make plants grow. The last tool is not commonly used, but I'll mention it anyways, it's the grass packet, makes your garden much greener, or, if you don't like grass, it pulls the grass out.
So now you've got your tools and first Pinata, what's next? if you own it already (at first the Pinata are just observing) you can experiment on it and change it's colors by feeding it with plants or food, or you can just breed it in order to get a few coins and bring your garden another Pinata being.
As you level up you achieve new Pinatas, Places to buy from, sour Pinatas (Which if you manage to make them your residents you get a nice experience bonus and an ability that can work nicely for you, for example, Crowlas can distract a certain type of foe entering your garden), more seeds, more items, and tool upgrades.
I had fun playing the game, but it might get you real pissed, it has some weird bugs, and you might waste lot of time trying to figure out how to get certain thing to happen.
So I suggest that only if you really feel bored and you can offer a lot of time, and, you're patient, only than I suggest you consider buying Viva Pinata.