How do I shrink Linux OS partition while it is in use

For guidance on how to attach images to a post see this thread.  [solved] put screenshot into post?

I decided to copy from my 1st post the section I am concern, mainly the Blue-Light Blue partition, I said on Option 1:

As stated above, run the Desktop with a Live CD or USB and rearrange the drive. The trouble here is that I will need to create, size and move partitions but for what I see the partitions listed are:

/dev/sda1     fat 32     /boot/efi (Mount Point)     with the Flag as boot (For what I read I should not touch it)

Then is listed the extended partition which has a Logical Partition within it using the same space as follows:

/dev/sda2     extended         931.01 GiB
    /dev/sda5     ext4             931.01 GiB         26.50GiB Used

Here is my main problem, how do I resize and move the partition sda5 (File System ext4) and make it, let say 100 GB (I think this should be sufficient to run Linux, am I right?). I think Mint is installed in this partition, is this correct? Or else where is Mint Installed?

Based on GParted this partition is the Blue one in the attached JPG. I would like to place this partition towards the left, besides the green one (boot), so on the right I will just have the light blue one, a large space that I could either leave it entirely or split it in two or three partitions for data saving.

How do I deal with this partition inside a partition?

Over the weekend I worked on this SSD and tried to rearrange the partitions.
From the picture above what I thought was that if I reduce sda5 to about 100GB I should be able to run Linux and end up with a partition for data saving and both separated. The initial idea was good but didn’t know the possibilities and the end result was not as expected.

After sda5 was resized I ended up with the extended partition sda2 light blue containing two partitions in dark blue sda5 and sda6 and the worse thing is that if I want to used sda6 I need to format it so I could have access to it. Based on what I read the extended partition sda2 created as extended contains the logical partitions sda5 and sda6 and it seems to me that is the way they will stay.

Now, if I want to use sda6 I have to format it, at present I do not have access to it (I just can’t save anything in there the partition is not recognised by Linux); but there is a 1.94GiB used that I do not have a clue what that is and neither know the effect on the system once I format sda6 because this 1.94GiB will disappear. Will still Linux run?

When I format this partition and I select Partition - > Format, what File System should I select? This large partition will be used only for data saving (pictures, videos, files in various formats, but no software will be installed in here), your advice will be greatly appreciated, thanks.

Well here should be what it looks like my SSD drive after this.

Edit: Convert link to picture to embedded picture ~mfleetwo

Let me confirm I understand all the steps:

I start the PC and open File that will show me a line with the following:
PCname:~$

Am I in the root directory or do I need to go further back? I am familiar with DOS and File is similar but not the same and wouldn’t like to write commands in the wrong place.

If opening File is in the root directory, I type

1. Create mount point directory.  mkdir /data
Shouldn’t I specify where the directory data should be made?

Then, on Step 2. Shall I write the /etc/fstab hit enter and write the following line and hit enter or make all one line and hit enter? O just write the line

/dev/sda6   /data   ext4   defaults   1 2

The above line is quite clear to me I think, I specify the partition (/dev/sda6), the directory (/data), the file system (ext4) and then “defaults and 1 2” I need to know what they do mean, at this stage I assume it is like saying default settings and the numbers should mean options.

Steps 3 and 4 are clear, after the data directory creation I mount it with 3 and make this directory open for everyone in 4.

Thanks for your time