need some help on replacing the compressor

You do that after installing the new compressor. Under full vacuum, any moisture from the humidity in the air will boil at 77 degrees Fahrenheit, then it can be drawn out by the vacuum pump. Moisture is the enemy of AC systems.

Here are some guides to help with this job:

https://www.2carpros.com/articles/replace-air-conditioner-compressor

https://www.2carpros.com/articles/air-conditioner-leak-detection

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

Be aware the refrigerant is extremely dangerous to work with. It can cause frostbite and blindness. Professionals wear gloves, safety glasses, and face shields.

Thanks for the help. I saw a video where before changing the compressor they were taking the pressure off from the low and high AC lines.

Normal procedure is to recover the old refrigerant with a special recovery machine. Most models then can recycle it when the cylinder is full. The fear at all the repair shops is they recover some alternative product that will contaminate the machine, the refrigerant in the storage tank, and therefore any system they recharge with that contaminated refrigerant. For that reason, most shops have refrigerant identifier machines that find and warn about anything that is not standard refrigerant, before they will work on a system.

Recovering the refrigerant is not the same thing as pumping it into a vacuum. Recovering just takes out what is in the system so it can be recycled, meaning filtered and dried. That leaves the AC system with no pressure and no vacuum. "Evacuating" the system means pumping it to a near perfect vacuum so any moisture will boil and be easy to suck out as a vapor. Some people do that for as much as two hours, and some for only twenty minutes. Thirty to forty five minutes is fairly common. At the end of the pumping, we watch the gauges to see if that vacuum holds. If it does not, there could be a leak, or there is still moisture in the system that is still turning to a vapor and expanding. To tell if there's still moisture in the system, pump it into a vacuum again for another twenty minutes, then observe if the vacuum is lost just as quickly as the first time. If it is, there is a leak. If it holds longer, moisture is the cause.

Moisture is a bigger problem when the system was open for a days or weeks, giving air time to enter and circulate. To reduce that, always cap the open fittings until the new parts can be installed.