Cubits are one of the many currencies on ManaCube. They're gained from voting, /gary (if you play at least 1 hour per day for 7 days straight), and buying them from other players. You've probably noticed that these cubits are very valuable. That's because cubits can be used as credits in the ManaCube store (1 cubit=1 USD). So many people will often save up on cubits to buy things from the store without having to spend actual money. I don't play factions so I don't know what the best way to get cubits are, but I know on both parkour and olympus you can buy cubits from other players for mana, and on survival you can buy from others for in-game money. Trading rates differ gamemode to gamemode and will fluctuate so it's best if you ask in the chat what the current rate is.
For factions, you can sell them for seasonals, money, etc. Keep in mind you cannot scam cubits.
Let's start off with money, typically a fair price for 1 cubit is worth 10 million, 0.1 cubit is worth 1 million, and 0.01 cubit is worth 100k. However, they can also be sold for much higher or lower prices depending on the buyer or seller. I wouldn't recommend spending cubits on money since it can be grinded using sugarcane farms.
Next is Seasonals; seasonals are items that can be brought over into new seasons. Some seasonals are really OP so look out for those. Unfortunately, staff had to remove the crates to follow eula, so now you can only get them by buying from other players, or killing a player using them.
You could buy other things such as gsets using cubits, which are fully maxed out enchanted diamond armor typically slayer kits since they are the meta right now. You could also coin flip your cubits to get more cubits, but I don't recommend it since it's a gamble. Finally, you could also exchange cubits for ranks.