to surface (a feeling)
The German word 'auftreten' is used to express the feeling of aflorar, which is the emergence or appearance of a feeling or emotion. It is often used in the context of emotions that are not immediately apparent but gradually become more noticeable or intense. For example, 'Das Gef├╝hl der Traurigkeit trat immer mehr auf' means 'The feeling of sadness began to emerge more and more'.
I can't perform.
This phrase is used to express the speaker's inability to perform (in a show, an event, etc). 'Auftreten' in this context is used to mean 'to perform'.
He will perform tonight.
This phrase is used to tell that someone is going to perform at some event. 'Auftreten' in this case is used in the future tense to indicate an upcoming performance.
When the problem occurred, I was not there.
In this sentence, 'auftreten' is used to mean 'occur' or 'arise'. It is used to talk about a problem that came up when the speaker was not present.