Confused about group and subgroup

[Info]

I have several class(1A and 1B for example) and subject, for example i have subject: A B C D, I want subject A and B to start together(which is fine with constraint), and subject C and D starting together, but do not overlap A B with C D, how should I set for the subgroup? The current attachment is just for reference for just in case.

[Volker Dirr]

Please read the chapter "Years, groups and subgroups":
https://www.timetabling.de/manual/FET-manual.en.html#id_12

Ask again if you still don't understand it.

[Info]

Please read the chapter "Years, groups and subgroups":
https://www.timetabling.de/manual/FET-manual.en.html#id_12

Ask again if you still don't understand it.

I have read but I do not really understand how to put

I am having trouble preventing two sets of activities from overlapping in the same time slot.

Current Setup:
Students: I have two groups, 1A and 1B.
Activities:
Set 1: Subject A and Subject B
Set 2: Subject C and Subject D

Current Constraints: I have used the "A set of activities have same starting time" constraint so that 1A and 1B start Subject A/B, C/D together.

I want Subjects A & B to happen simultaneously (split between the two groups) in one block, and Subjects C & D to happen in a different block.

Currently, FET sometimes schedules all four subjects (A, B, C, and D) in the same time slot. I need to ensure that the "A+B" block and the "C+D" block never overlap.

The result should be:
Slot 1: 1A does Subject A | 1B does Subject B (Simultaneously)
Slot 2: 1A does Subject C | 1B does Subject D (Simultaneously)

How do I achieve this?