“If you have any questions regarding Adele or her performance, please feel free to contact me.”

You're writing a letter of recommendation for a former employee who is applying for a new job. You have finished writing most of the letter, and now you're concluding it. You write:

If you have any questions regarding Adele or her performance, please feel free to contact me.

have questions regarding (something)

"Questions regarding ___" means "questions about ___". "Regarding" is a more formal version:

I have a question regarding my bill. Is there someone I could speak to about it?

(someone's) performance

The word "performance" refers to how well someone does something. People often talk about a person's "job performance", which is how well someone does their job:

I've been extremely satisfied with his job performance.

In the example at top, the writer doesn't use the phrase "job performance", but that is the kind of "performance" she is talking about. The sentence means "If you want to ask about Adele or how well she did at her job, please contact me.

feel free to (do something)

When you want to give people permission to do something, you can say "feel free to ___." This is a formal phrase that you usually use with people you don't know very well, or with large groups:

Feel free to take one if you want it.

Feel free to ask questions at any point.

The phrase "feel free to contact me" is really common.

contact me

To "contact" someone means to call, email, or send a letter to them. Those words are all specific, but "contact" can mean all three.

In more casual speech, the phrase "get in touch with ___" can be used to mean "contact ___".