If your goal is to create your own workload rather than using the oltp workload you should start considering which business processes you want to simulate and which SQL statements are used for each. Rwloadsim can be programmed to execute any SQL statement and your simulation is likely to at least consist of a mix of queries and dml. An important aspect is the random nature of a simulation, where rwloadsim has several ways to generate random values for both integers, doubles and strings.
For the number types, you can use the function uniform to generate uniformly distributed numbers or erlang, erlang2, erlangk to generate positive numbers with a specified average; a suggested description is the Wikipedia article on the Erlang family of continuous probability distributions.
To create random strings, you can include the ovid2.rwl file, which has two public functions that create respectively a string consisting of a given number of words or a string of approximately some length. See the rwlman page on ovid2 for details.
The next step in your own workload simulation is to create rwloadsim procedures that implement your business functions; each procedure should implement one business function. On top of these, create a random procedure array that executes your procedures with the probability required.
The core of your rwloadsim program will then be a run command that starts a number of threads executing a randomly chosen procedure at a certain rate using a control loop. When a procedure (that has SQL or has the statistics attribute) is started, it will ensure a database session exist, which in the common case of a session pool will mean acquiring a session from the pool. Upon exit from the procedure, the session is returned back to the pool.
Using the rwloadsim repository and the -s option to rwloadsim, statistics about execution will be gathered. This can subsequently be used to create reports including graphs by the help of gnuplot.
The complete example is created based on exactly the approach, and is therefore good as a starting point for you own workload.
The provided oltp workload is an example of a workload that uses many features of rwloadsim in combination with shell scripts. If you want to understand this in details, it is recommended to start with the core shell script, oltpcore available in the bin directory.