feel free to (do something)

When you want to allow people 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 call me with any questions.

This phrase is often used in business situations, with coworkers, employees, bosses, and clients.

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.

contact (someone)

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 ___".