Chisa, here are some general hints for the game, some of which may be appropriate for your question. The boxes are part of a puzzle.
1) Read every pop up screen and consider taking a screen shot of it for future reference. I would say about half the questions I see are from people who missed what a pop up said. (Your question does
not fall into this category!) As you deal with the three boxes, a thirst for knowledge from pop up screens will come in very handy.
2) At first, be conservative with coins unless you can buy some with an in-app purchase. Consider deferring home improvements for a few days. Catch and sell bugs as akard said. Spend your time exploring all the options in the town businesses, but don't necessarily jump right in buying everything.
3) If you run into something you don't understand, try picking it up. If you can't pick it up, use a tool on it. You only have 5 or 6 tools, so just use them each in turn until you find one that works. If you can't pick it up and you can't use a tool on it, consider that it may be a permanent part of the game environment.
Everyone seems to want to break open that big rock on the eastern edge of the town area, just north of the southeast forest. It's part of the scenery. Don't waste your time.
4) If you have something in your inventory or storage that doesn't fall into any of the major categories (seed, mineral, bug, clothing, fruits/veggies) or you have something that's just unusual, take it to the store proprietors. One of them may want that item. Try everyone until you find someone that's interested.
Hope this helps!