You are expressing a desire to do something. 你在表达很渴望做某事。

Here are some examples: 这里有一些例子： 

"I wish I could sing better."

 我希望我能唱得更好。

"I wish I could settle the argument."

 我希望我能解决这个争论。

"I wish I could sail around the world."

 我希望我能环游世界。

"I wish I could remain calm during all of this."

 我希望我能在这一切中保持镇定。

"I wish I could remember his name."

 我希望我能记住他的名字。

"I wish I could replace my old car with a new one." 

 我希望我能用一辆新车取代我的旧车。

"I wish I could play outside."

 我希望我能出去玩。

"I wish I could go to the game with you."

 我希望我能和你一起去看比赛。

"I wish I could write better."

 我希望我能写的更好。

"I wish I could own my own business."

 我希望我能拥有自己的事业。