What's up ? = What's wrong ? / What's happening ?
Your eyes are red and swollen Jack. What's up ?
Take someone's word = Believe even if there's no evidence
I'm sure the teacher will give us a quiz tomorrow. You can take my word.
It's a good job that ... = It's fortunate that ...
It has started to rain now. It's a good job that we brought our umbrellas.
Words failed someone = was unable to speak
When I knew that my brother had an accident with my car, words failed me.
Make up one's mind = make a decision / decide
Come on ! Make up your mind ! are you or are you not coming with us ?