'Ask' is used a) when you put a question to someone:' We asked the teacher' b) When you seek an answer: 'We asked a question'. c) When you seek information:' We asked directions' ( you can also use 'for' here) d) when you make a request of someone: 'I asked him to help me'.
'Ask for' is used when you try to obtain something by requesting. ' He asked for a drink.