Here are some pictures with the explanation of some funny English idioms!
1. Bob's your uncle - this means 'it's as simple as that'. It can be said in a situation where you are explaining a simple set of instructions and add 'Bob's your uncle' at the end.
Example: To make a cake, you mix flour, eggs and milk and Bob's your uncle!
2. A piece of cake - something is very easy to do.
Example: That exam was a piece of cake!
3. Head in the clouds - living in a fantasy
Example: I don't think it's possible to have a serious conversation with her, her head is always in the clouds.
If you would like to make some examples below, please feel free! :)