How to verify ISO file

[Rusty Relic]

Computer: Dell Optiplex 380 running Linux Mint 19.3 Mate
Could someone kindly point me to a step by step procedure for verifying the ISO image for Mint 21.1. I am not a terminal user nor am I a computer geek. I have tried using Google and so far haven't discovered anything I thought was usable, I suspect mostly because I don't understand the terminology. In the past I have run Mint Cinnamon 17.3 and currently running Mate 19.3 without doing any verification. Is it really necessary?
In reading the 21.1 release notes it appears that the new version has a more user friendly procedure for verification once it is installed and running.
TIA.

[karlchen]

The official instruction document: Verify your ISO image

Is it really necessary?

Yes, it is, else the official download pages would not ask you to do so.
Any data transfer can fail (partially or completely). Complete failure may be noticed easily, because you simply do not get any download file.
It is the partially failed downloads, which cannot be detected without following the verification steps.
Wasting your time on trying to install from a(mildly) corrupted ISO image file would be frustrating.

And there is another good reason to take the time and pain of verifying the downloaded ISO image: Make sure that you really downloaded the genuine Linux Mint ISO image file, which you wanted to download and not a maliciously modified ISO image, which only pretends to be the desired Linux Mint ISO image file.

[Rusty Relic]

Hmm, I guess I got the response I deserved since I didn’t specify exactly where I am having trouble.
In the instructions under the heading ‘Integrity Check’ it shows ‘sha256sum -b yourfile.iso’ in a yellow bar; I assume that means run that code in the terminal. I tried replacing ‘yourfile’ with ‘linuxmint-21.1-cinnamon-64bit.iso’. I got an error message “No such file or Directory”. So, what am I doing wrong?
Since I am not a terminal user I am wondering if it’s some terminal protocol that I am violating that’s causing the problem. What other issues am I going to run into trying to complete the rest of the instructions in the verification section?
Restating what I said in the original post that I am not a terminal user. The only time I have used the terminal is when I did a copy and paste some time ago when I couldn’t get 19.3 to recognize a consumer level HP printer and someone on the forum spelled out what to do. I am not looking forward to the prospect of having to deal with printer connection issues again.

[Pierre]

Yeah - - you do have to Run that command in Terminal

But
it also has to be in the same folder as your file resides in.
or you will get that error that you saw , , ,

so, try again, with an R/click on an vacant area of the folder,
- where you have placed that ISO into - usually /downloads/
then select the option to "open in Terminal" . .

then, try again with those cli commands.

[Rusty Relic]

Thanks Pierre
After a stupid mistake or two I now have the sha256sum verified. Now to document the procedure and save it. Saving it in gray matter memory isn't reliable any more - eight decades of wear, etc. . Then on to do the rest of the verification or at least try to.