|Re-creation of wax tablets [link]|
A shallow wooden or ivory frame filled with soft wax could be written on with a stylus; the other end of the stylus was a flattened blade shape that could be used to smooth out the wax for re-use. The beeswax would be mixed with plant oils and/or carbon to create a more legible surface. Tablets were often not simply one piece; They could be turned into leather-laced "booklets" where the outer tablets held wax on the inside, and inner "pages" would have wax on both sides.
Wax tablets were great for business records. A hospital in Enns, Austria used multiple-page wax tablets (that still exist) to track some financial records. Payables due would be printed on parchment and stuck to the left side; money received would be written on the right side in wax and added up. The impression would store indefinitely—so long as you didn't let it get hot.
Tablets were also ideal for transactions that did not need to be kept long-term. The impression could last for a week or month or season, and then warmed up and smoothed over for the next set of transactions off the boat.
Here's an extensive directory of links to pictures of tablets from across the centuries.