How does the repeat signs work, which are implemented in BiaB ? For me it's quite confusing , because the counting of the bars is strange and it clashes with the chorus length. Is there any tutorial or video about using the repeat function?
Traditionally, the way you structure your song is using the Start, End, # choruses - found at the top of the screen in the toolbar area to the right of the song title / style fields. A 'Chorus' is once through the song form, as it is in jazz. If your start bar is higher than 1, then you have an Intro. Additionally, in the Song Settings dialog (button just to the right) you can set a Tag ending which will play after all the choruses.
There is also the option (that was added more recently) of adding repeats and 1st/2nd endings - these are mainly intended to allow you to print out a chart similar to what you would see in a fake book. To add a repeat you can right-click in the Chord sheet and select 'Repeats/codas/endings'. There is often confusion about the repeats, because you can toggle "Fakesheet mode" which hides the repeated bars if it is on/checked. But Band-in-a-Box is still generating music in the repeated bars, and you can still have a melody or solo happening which may be different in each repeat. But if Fakesheet mode is on those bars are hidden from view. There is a video here that goes over this (this is several years old but still applicable):