can someone pls walk me through how to back up my mac? I have a new one and believe I need to back up the old one first?

In addition to the excellent advice provided by ku4hx, I thought I'd provide some additional details regarding transferring your data from your old Mac (you didn't mention if you're coming from Windows or Mac, BTW) to your new one:

First, familiarize yourself with Migration Assistant: Transfer to a new Mac with Migration Assistant - Apple Support

Next, decide how you want to transfer everything. There are, essentially, four means of transferring the data:

• • Via WiFi (this is what the instructions tend to lean on the most...however, it's far from the fastest method, and is subject to WiFi signal dropouts that can corrupt the flow of data).
  • Via Time Machine External Drive - This method is tried and true, and I used to use it every time I needed to run Migration Assistant. It's rock solid, but not the fastest.
  • Via Ethernet Crossover Cable - This is a bit faster than the Time Machine backup.
  • Via Thunderbolt 3<-->Thunderbolt 3 cable. This is the fastest method, and the one I've used for my last two transfers. You simply connect the cable to a Thunderbolt port in each Mac, then run Migration Assistant. Here's the cable I use: Thunderbolt 3 cable

I'm not a fan of the WiFi transfer as it's slow and subject to errors, unless you have a very strong WiFi signal and both Macs are connected to the same WiFi network. (Even then it's pretty slow).

The Ethernet crossover cable method is fine, but it would require at least 1, most likely 2, adaptors, as Macs haven't had ethernet ports in quite a while.

As ku4hz mentions, make sure you back up your old Mac first before migrating.

Hope this helps.

There are two processes you need ro do. One is to transfer your data from the old Mac to the new one using Migration Assistant. I will describe the process below. The second process is to back up a computer's data. To do that you use the Time Machine app to back up to an external disk which is connected to the Mac with a USB cable. To do the Migration Assistant transfer, follow the steps below.

Migration Assistant is very easy to use. Be sure to read and follow its instructions.

You first begin by starting the process of setting up your new computer. You will be asked if you wish to transfer files. Respond YES and follow the instructions you will be given.

·      You will be told to turn both computers on and activate Migration Assistant in the old computer.

·      The computers should be connected with a cable to facilitate the transfer. Wi-Fi is not suited for a transfer of so much data and corruption often results. If you must use it, make sure the two computers are located close together.

·      You will be given several options of what to transfer. You will likely want to transfer your settings and preferences.

·      You can transfer all or none of your files. You do not have an option to select certain files to transfer. If you wish to do that, then do so manually. You can transfer all or none of your installed apps. Some people elect to download fresh installations to the new computer instead.

·      The old computer's operating system will not be transferred. No data from the old computer is erased.

·      Allow for up to an hour for the transfer process to complete once you start it.

·      It should set up the new computer the same as the old one.

·      When that is successful, you can log into the new Mac with the old User Account name and password and delete the brand-new user or leave it in place as a second admin account.

Once the transfer is completed, you should immediately back up the new computer as mentioned above.

Enjoy your new Mac.

I hope this is helpful. Good luck.

Back up your Mac with Time Machine - Apple Support

Backup both.

As to setup, turn it on and when the setup screen appears, just answer the six or so questions and you're done.