In German language there are words als and wann that can often be confused. They are both translated to English as when, so that's the main cause of confusion. But, there are rules when each of them is used that will help you to make a clear difference.

We use als when there was one such event in past and we talk about it. For example, if we want to say that something happened in our childhood, we will use als, because there is only one childhood for everybody's life.

Meine Mutter spielte mit mir, als ich ein Kind war. ----> My mother played with me, when I was a kid.

Meine Schwester ist nach Frankfurt gegangen, als sie 17 Jahre alt war. ----> My sister went to Frankfurt when she was 17 years old. she was 17 years old only once in her life

We use wann when we talk about some event that can happen multiple times, in different years for example. For example, when we want to say that something happened when we were at the house, we use wann, because we are at house almost every day, it's a repeating event.

Ich habe Angst, wann ich zur Arzt gehe. ----> I am afraid when I go to the doctor. a person goes to the doctor sometimes in her life and can go as many times as needed, it's not a special event

Ich bin glücklich, wann ich mit meinem Bruder spiele. -----> I am happy when I play with my brother. you can also play with your brother more than once, it's not any special one time occasion

Important to note: when als/wann or any other conjuction comes in the middle of the sentence, before it always goes a comma