All you needs is a command terminal and access to the file to transfer to the SD card.
If all is well the linux you have running from the USB stick has internet connection, so you can go to the repository and download the file on to the USB stick. Then open the command window with "ctrl - t" or "ctrl - alt - t". At the command line you can then type the commands, but make sure you select the right target.
So first connect the SD card reader/writer with the SD card inserted into the computer. This will mount the SD card automatically if all is well. At the command prompt type "lsblk" and then enter. This will list the block devices.
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 3,7T 0 disk
└─sda1 8:1 0 3,7T 0 part /home/peter/Data
sdb 8:16 0 111,8G 0 disk
├─sdb1 8:17 0 55,9G 0 part
└─sdb2 8:18 0 55,9G 0 part /
It will show something like the above. The SD card might show up as sdc ..... 1G 0 disk and the line below will show ---sdc1 .... 1G part .......
This gives you the name of the device you need to work with.
Maybe it is best to save a screen shot of the listing and post it here. (You can use the PrtScrn button to make the capture and then post it here)
We can then take it step by step, just to keep your system safe. But it is about my bed time, and tomorrow I'm a bit busy, so be patient