Sperling Task how do i creat the stimuliset?

My Task is to create the sperling task with the builder.
Quick summary:
presenting subjects with brief presentations (50 msec, followed by a mask) of three rows each containg three random letters from the alphabet. one of the rows is marked with an arrow. Afterwards participants have to report the latters from the row with the arrow. Then they get a feedback if they were right or wrong. Subsequently the task is starting again.

Questions:
how do i create the stimuli set?
with excel?
unfortunately i’am not familiar with the programm

To find any of our suggestions useful, you will need to cross that threshold first. I suggest you start with Jon Peirce’s Stroop task tutorial on Youtube.