fragen have the meaning
Is there any rule, when to use each of those words ? Or are they complete synonyms and can be freely switched ?
"Stellen" actually means "to put". You can combine it with "eine Frage".
- "eine Frage stellen" = "to ask a question", or literally "to put a question"
- "fragen" = "to ask"
Ich frage. - I ask. / I am asking. Ich stelle eine Frage. - I ask a question. / I am asking a question.
Ich frage meine Mutter. - I ask my mum. / I am asking my mum.
Ich stelle meiner Mutter eine Frage. - I ask my mum a question. / I am asking my mum a question.
(Side note: "eine Frage" is the accusative object, "meiner Mutter" is the dative object - the person who "receives" something, is always in the dative case.)