This is an example process to download and install Raspberry Pi Operating System.

go to:
https://www.raspberrypi.org/software/operating-systems/
Download Raspberry Pi OS with desktop
Direct link as of 20201224:
https://downloads.raspberrypi.org/raspios_armhf/images/raspios_armhf-2020-12-04/2020-12-02-raspios-buster-armhf.zip

To show which devices are connected to your machine:
lsblk -p
choose the appropriate card: yourcard
you can also use df to see disk sizes, space used, space free.

umount /dev/yourcard

If there are more than one partition on the card, use fdisk to reconfigure to a single FAT32 partition.
sudo fdisk /dev/yourcard
d (delete partition)
d (delete partition, continuing until all partitions are deleted)
n (create 1 new partition)
p (enter)
1 (enter)
default (enter)
default (enter)
v (enter)
w (enter)
sudo shutdown -now

umount /dev/yourcard

cd to the location of your image file
sudo dd bs=4M if=2020-12-02-raspios-buster-armhf.img of=/dev/yourcard

or combine the unzip and dd processes:
cd to the location of your image file
unzip -p 2020-12-02-raspios-buster-armhf.zip | sudo dd of=/dev/yourcard bs=4M conv=fsync status=progress 

Example Result:
unzip -p 2020-12-02-raspios-buster-armhf-full.zip | sudo dd of=/dev/sda bs=4M conv=fsync status=progress

[user@manjaro Downloads]$ sudo unzip -p 2020-12-02-raspios-buster-armhf-full.zip | sudo dd of=/dev/sda bs=4M conv=fsync status=progress
[sudo] password for user: 
8773435392 bytes (8.8 GB, 8.2 GiB) copied, 487 s, 18.0 MB/s
0+113072 records in
0+113072 records out
8787066880 bytes (8.8 GB, 8.2 GiB) copied, 523.055 s, 16.8 MB/s

sync
sudo shutdown
remove sd card, it should be ready to boot.

Replace old sd card with newly created sd card in pi.

Power up.

Note down the IP address in records.
Go through setup:
Set Country, Language, Time Zone
Set pi password
Fix screen size if necessary
Connect to wifi
Update software
Restart

Preferences/Raspberry Pi Configuration
change password
change hostname: PiOS-20201227
Autologin Disabled
reboot, login with new password

sudo adduser main
(set password)
sudo adduser dailyuser
(set password)
sudo adduser main sudo

reboot, login as dailyuser
sudo deluser -remove-home pi

Preferences/Raspberry Pi Configuration
enable SSH and VNC
reboot

Applications to install:
sudo apt install thunderbird xscreensaver firefox-esr librecad foobillardplus freeciv midori calibre exfat-fuse exfat-utils

sudo wget https://yt-dl.org/downloads/latest/youtube-dl -O /usr/local/bin/youtube-dl
sudo chmod a+rx /usr/local/bin/youtube-dl
hash -r