Let's say you have a firm with these two simple journal entries:
This will be the benchmark for your exercise.
When you are done with the firm, click on "Challenges", "Manage Exercises" and then "New Exercise".
Fill in the details of the exercise, and select the firm that you prepared as benchmark.
After saving, create the transactions (operations to be recorded on the journal) by clicking on the button "Create Transactions from Benchmark Firm's Journal Entries" to import them from the journal entries (you will automatically invited to the challenge).
Then, edit the transactions at will, giving enough information to your students to prepare the entries in the right way. You can add hints for each transaction, if you want.
You can use Markdown syntax for the descriptions and the entries.