Growtopia is a super open-world game that has endless possibilities. Since sandboxed, tuning the game to obtain full satisfaction is left to players will here. Though Growtopia runs on the collecting, harvesting, and building items, players can create or play with others' created worlds. In-game, you can choose to do anything from being a farmer, chef, sportsmen, adventurer, etc.
Starting with the basics, new players walk into a tutorial with bare hands, where they can only smash blocks and dig deep to collect seeds. These are supposed to grow trees, harvest, and sell them for gems. If not, breaking some blocks may cater to the gems directly. You may go to a marketplace to purchase other necessary tools or trade-off unwanted stuff for more gems.
Also, you can try using the recycle tool for converting unwanted items into gems. Since the game runs on a single currency system, you may want to gain as much of the possible. While the UI seems buggy and blocky, it's essential to keep the game at fewer data and be accessible for everyone. First-time players may confuse with the 2D UI of Growtopia, and also with the tons of tools given on the screen initially, but they get accustomed after a prolonged period of playing.
Though Growtopia's essence lies in building blocks and collecting gems, players can actually explore a universe of opportunities. Players can make mini-worlds having their own buildings within, rules and prizes, and let others tinker in. If not, they can form tasks, create puzzles, etc for others to solve and reward them.
Also, players can create worlds not just on land, but also in space, or create new items completely based on their imagination. And if they're good enough, they can be traded for gems. Join the other explorers, fly on a dragon, make friends with wizards, etc and even battle against other players in the realm.
At any given time, there are tens of thousands of players online. So you'll never see a lack of new worlds and challenges making up and the marketplace empty. Players here get better on advice from others and is a recommended path to learn the game from Growtopia's chat, online forums, and other means of communication set.