The main objective in Nextbots: Backrooms Sandbox is to explore a vast space sandbox starting from a military base built on an asteroid, while defending yourself against incoming alien monsters and earning points through successful battles to climb the leaderboard.

Unfortunately, you cannot build your own weapons in the game. However, you will find various guns spread across the rocky surface of the asteroid that you can use to defend yourself.

The portal gun allows you to strategically summon enemies to test your skills or set up traps. You can use it to create portals that transport enemies to different locations, giving you an advantage in combat.

Yes, there is a single-player mode available where you can explore the vast space sandbox and defend yourself against alien monsters without the need for online multiplayer.

Absolutely! You can play with friends online and compete with them to see who can earn the most points and climb the leaderboard the fastest.

There are no specific power-ups or upgrades mentioned in the game description, but you can earn points through successful battles and strategic gameplay which may unlock new content or features.

The game seems to offer a good balance of challenge for beginners, as you start from a military base and have access to various weapons. However, the alien monsters may pose a significant threat, so players should be prepared for intense action.

The game description does not mention a specific storyline or narrative. It focuses more on exploration, combat, and competition, allowing players to immerse themselves in the vast space sandbox environment.