The Store (yes, it's an Item-Shop) is a feature of Creativerse where players can purchase Coins for (real) money, which can then be spent for what the item shop or game has to offer in exchange.
The Store mainly features unique crafting recipes and packs of items and/or blocks, like Explosives, Machines or rare materials like Arcstones.
Since Creativerse is free to play in principle, the servers and further development of new features have to be financed in some way, so to support the game and the developers, players can do it by buying coins for the game for real money in the Store (and/or by buying DLCs via Steam).
Currently the offers in the Store are all purely optional and won't affect the gameplay or progress within the game in any way. Many crafting recipes can be unlocked by collecting materials and crafting basic items.
Even though the "Pro" DLC offers useful features like world options, glider and flashlight, the bundles and packs from the Store are nearly all purely decorative and most often merely sport alternative designs of common blocks and craftable stuff.
Swords that are part of some themed recipe bundles for example never inflict more damage points than "free" swords, and their crafting recipes do not require significantly "cheaper" or much less rare ingredients either.
In the Store TAB you can also redeem item bundles via redemption codes that are usually temporarily valid and will often be announced on the official forums or via Twitter.
Some redemption codes, like those given by Let's players on YouTube, might still be active; so you might want to try to redeem them right now: http://steamcommunity.com/app/280790/discussions/0/1318836262665615633/
The Store currently (April 2017) offers:
- Recipe Packs for store-exclusive Fireworks, Premium building blocks and items like furniture or interesting looking swords. Once bought, these recipes are permanently added to your crafting menu and will then be available on all Creativerse gameworlds from the start, even on worlds where the option "world bound recipes" is disabled ("Pro" world option). Additionally to that, one item kit with already crafted examples for the recipes can be claimed on one single gameworld of your choice too
- Item Packs (that come without crafting recipes) can be bought in the Store and can only be claimed on one specific game world, like with Machines, Explosives, Lighting or rare materials like Arcstones
- and Coins of course, purchasable via Steam Wallet.
The "Pro" DLC however - which is not part of the Store - includes more gameplay-relevant options, like the possibility to own many more gameworlds than just one, to use a glider and a flashlight, and to change options of your gameworlds in a way that will influence the gameplay experience significantly somehow (like easy or hard combat difficulties, passive creatures, prohibiting PvP, etc.).
Creativerse is a sandbox game intended for building and playing together with friends, where even PVP is only for friendly competition and there is no specific game goal to achieve after all, different from an MMORPG.
Block kits for Blueprints are also not part of the Store, but will still be paid with Coins. These block kits contain all blocks and materials required to build the standard buildings that Blueprints suggest (while the Blueprints themselves are for free) and can be bought by clicking the according "get kit" option in the "Blueprint" TAB below the chosen Blueprint. This will also unlock the according cornerstone right away, so no materials will have to be collected to craft a cornerstone.
Another thing you can buy for Coins are Claims. Areas can be claimed by player by trading in certain materials (mainly ores), but alternatively Coins can be spent too. And while only 6 (+2 for "Pro") claims can be "bought" with Ores, you can buy up to 24 (+2 for "Pro") claims on each single gameworld when spending Coins.
Players who had bought the game during early Early Access before Creativerse went F2P on November 11th 2015 have received Coins for the Store plus the Gold Pack as a reward. Later on they have received the "Pro" DLC completely for free, which also applied for all players who had bought any amount of Coins for money before July 2016.
For christmas 2015 there was another Coins giveaway. To celebrate the launch / release of Creativerse, additional Coins were thrown in as a gift for everyone who bought the "Pro" DLC during this timespan, etc.
Similar occasions might come along in the future once again, so if you are interested, you should follow the official forums or the Creativerse twitter, especially on patch days.