Use "wish" to say that you want a situation to be different than it is. You can use "wish" for situations in the present and in the past.

=> Present: To talk about the present, use: wish + verb in the past tense

Examples:
▶ I wish I had a summer house (I don't have one).
▶ I wish I spoke Chinese (I don't speak Chinese).
▶ I wish I were* rich (I'm not rich).
▶ I wish you were* a lawyer (You're not a lawyer).

* After "wish" use "were" instead of "was". This is the form of the verb "to be" that's used when situations are imagined or unreal. It's called the subjunctive.

To say that you are not happy with the current situation and that you want somebody else to do something about it, use: wish + would (or the contraction 'd) + base form of the verb

Examples:
▶ I wish you would lose a few pounds.
▶ I wish that guy I met at the bar would call me!
▶ I wish they'd stop talking during the movie.
▶ I wish it would stop snowing.*

*In this case, you need Mother Nature to help you change the situation!

=> Past: To talk about situations in the past that you regret or are not happy about, use: wish + had (or 'd) I hadn't + verb in the past tense

Examples:
▶ I wish I hadn't agreed to this.
▶ I wish I'd followed your directions.
▶ I wish I hadn't eaten that sushi.
▶ She wishes she'd gotten into the University of Pennsylvania.