Flow is the state of complete absorption where performance feels effortless and time seems to change. You cannot switch it on, but research suggests some conditions make it more likely.
Commonly described conditions:
A balance between the challenge and your skills; too easy feels boring, too hard creates anxiety
Clear goals for the session or the moment
Immediate feedback, so you know how you are doing as you go
Attention on the task, not on outcome, judgement or the crowd
One practical takeaway for training: set process goals that sit just beyond your current level, such as holding form on the last rep, or hitting a target split by feel. That keeps the challenge-skill balance in a useful zone.
Sessions that are always very easy or always overwhelming are less likely to produce that absorbed state.