Trials in Experimaker are automatically generated from stimulus sets linked to the block. If you’d like find control over which trials are generated, you can set block order to fixed and sort your stimuli accordingly. The 1st stimulus in each stimulus set linked to the block will be used to generate the 1st trial; the 2nd stimulus in each stimulus set will be used to generate the 2nd trial, etc. This is explained in greater detail in Stimulus Set Structure.