After you've added an exercise you will see several fields to add in specific exercise instructions. Sets will always be the first field presented for every exercise and then the next 1-2 metric fields will be presented based on the Exercise Library rules. For example:

Deadlift: Sets - Reps - Weight
Push Up: Sets - Reps
Rowing Machine: Sets - Time - Distance

The programming tool was designed with a single line as the default for exercises, similar to Google spreadsheets, so that you can view more of your exercises while scanning through a workout session during programming and tracking with the web app. The one limitation with the single line view is that it only allows you to write reps and weight, for example, for all sets. In the picture above Deadlift is programmed for 3 sets with 10 reps for each set. If you would like to adjust the reps and/or weight for the other sets you can click the dropdown arrow to the right of the metrics to expand the view:

If you have programmed sets to have different reps and weight, using this example, and click the up arrow to close the view you'll notice an asterisk above the reps and weight numbers (picture below). This is your visual cue that this is an exercise with different reps and weight for each set. To also help with avoiding any confusion, when you go to track this exercise during a workout session the exercise will be expanded to view all sets as a default (matching the picture above).