A cheque is used to pay people. Instead of sending cash through the post and risking it getting lost, a safer way is to post a cheque and have the money transferred directly from your bank-account. That way, if the cheque gets lost, it can be cancelled without any loss of money.
A cheque is filled with details of the transfer such as the drawer's account, the amount of money to be paid, and the date. It is then signed by the person paying the money (called the drawer), and the cheque is then given to the person to be paid (called the drawee). The drawee can then submit it to their bank, who will handle the money-transfer across the accounts. Some banks may have additional rules about cheques, such as blocking transfers if the cheque is too old.
Cheques also have an "Or Bearer" option, which means that the money can either be transferred to the specified drawee, or given as cash to whoever gives in the cheque (even if the cheque is for a different person). This is useful if the drawee doesn't have a bank-account, but is otherwise considered a security risk. So unless required, it is recommended that you disable the "Or Bearer" option (eg. by cancelling the "Or Bearer" sentence in USBC cheques).
Cheques were introduced into SSS by the SSS Bank to help people pay money remotely without risk of losing it in the post. The idea is based on the real cheques used by non-SSS banks.
The first cheques were issued by the then-Banker Hippo (Cheetaplaza) in 2009. This was when the SSS Bank was still the only existing bank; private companies hadn't started yet. This meant it was easy for the bank to manage transfers as there was no question of money getting transferred from accounts in other banks.
The first cheques had fields for both the drawer and the drawee's names and account-numbers, as well as the amount of money to be paid and the drawer's signature. The design were later revised so that it did not require the drawee's account-number to be specified; the reason for this was that people found it hard to remember the account-numbers of every single person they had to pay. In any case, the drawee can always tell the bank his or her account-number directly, at the time of cashing the cheque. The new design also included a field to write the amount to be paid as text as well as numerically, to avoid mistakes due to mis-reading of the amount.
The old SSS Bank cheques were simply forms on plain pieces of paper. During her Banker term (2013-14), Eesha (Callisto) introduced new cheque designs that had decorative illustrations on them. This was done at the same time as releasing the new SSS banknotes.
In 2014-15, Banker Pragnya (Candor Chasma) removed cheque support from the SSS Bank, as part of the many reforms to reduce the Banker's workload. To fill in the gap, the private banks of the USBC came together and set up a new cheque standard, which allowed cheque-transfers to easily happen between accounts even across different banks. As of October 2015, USBC cheques are being provided only by Cheetabank, with other banks yet to implement their cheque-transfer systems.