I have the Wifi model and always do the programming from my phone or tablet, so I can't speak to your model specifically. The Wifi didn't exist two years ago, so you're either on the 'old' Gen 2 D controller or the updated Gen 3 'D' controller. I think the Gen 3 'D' controller just came out, so I'm going to assume you're on the 'old' controller. Manual:
https://www.smokin-it.com/v/vspfiles/files/DigitalManualold.pdf Reviewing the manual, it looks like the programming for your controller is conceptually the same as for the newer Wifi controller. You can program 6 steps with the program determining the cook/box temperature to use for the duration of the step and the criteria for when the current step should end and the next one should begin. The cook is over when the controller runs out of programming. That could be after step 1 if step 2 isn't programmed or after step 6 if all 6 steps have been programmed.
For each step you have to define what will cause it to end. You can tell a step to end after a certain amount of time (in hours and fractions of hours) or after the food probe hits or exceeds a specified temperature reading. Each step must be one or the other and cannot be both. However, each step is independent and can be different from the prior or next. (example: Step 1 might set the cook/box temp to 235 and be programmed to end when the food probe has a temperature reading of 195 or greater. Step 2 might then set the cook/box temp to 140 and be programmed to end after 2 hours. The total smoke/cook time will be however long it takes for the food probe to register a temperature >= 195 plus an additional 2 hours. With no step 3 defined the controller will consider the smoke/cook complete.) You do want to make sure that any steps you're not using are set to a cook temperature of 0 and with a time (vs food temp) of 0, as well.
When you are about to begin a new cook, turn on the smoker, and press and release the Set button one time. It's important that you just press and release the set button. If you press and hold the set button for 2 seconds then the controller will do something entirely different than described below.
If things work as the manual describes then you have two 'windows' on the face of the controller. The left window will say C-1 and the right window will show a number. Since the manual doesn't seem to clearly and consistently define what the C means in C-1, let's assume from here on that it means Cook Temperature. The Cook Temperature is the target temperature inside the smoker. The 1 means this is step 1. The number at this point is the Cook Temperature you want for this step. So in the prior example, you'd use the +/- buttons to change the number to be 235.
When you have C-1 set to 235 press the Set button again. Now the left window should say E-1. The right window should either be a capital 'F' or a lower 't'. In this case the 'E-1' means you are still programming step 1 and you are specifically defining how it will end (E). If you choose 'F' then you are saying you want the step to end when a particular Food Temperature is recorded by the food probe. If you choose 't' then you are saying you want the step to end after a specified period of Time. To continue with the example, you'd want this set to F.
Once you have the End criteria (temperature 'F' or time 't') selected, press the Set button again. As a confirmation of what you selected, the left window will now show either F-1 or t-1. For our purposes, it should say F-1. This tells you that the number on the right is the Food Temperature you are setting for the food probe to detect and trigger on. To stay with our example, use the +/- buttons to set this to 195.
Once you have the left window saying F-1 and the right window saying 195, press the set button again and it should take you to the second step of the program which will be indicated by the left window displaying C-2. Program step two by repeating the steps you just used for step 1. [Change the right window to show 140 (left window shows C-2), press Set, change the right window to show 't' (left window shows E-2), press Set, change the right window to say 2.0 (left window shows T-2], press set.]
At this point the left window should be showing C-3. Follow the exact same steps you just used for C-2 to set the Cook Temperature to 0, to End by time, and set the Time to 0.0 hours. Do this for C-3 through C-6.
With the program now fulling defined the green light should come on to indicate the element is on, the left window should show a temperature, and the right window should show a time which all indicate the program is running.
Your prior message indicated you don't normally see the 't' or 'F'... if you don't ever see that following the instructions above, please elaborate what you do see as you try to follow these instructions and maybe we can figure out what's going on.
