1. ask sb about sth : 问某人关于某事。

They asked me about the new teacher’s name.
他们问我新老师的名字。

2. ask sb to do sth : 叫某人做某事

He asked us to wait for him at the gate. 他叫我们在门口等他

3. ask for sth ：请求帮助

He asked for some water. 他要些水

They asked me for help. 他们向我求助