While Linux is great for servers and containers, it is a little bit a hassle to work with. Especially when using the command line. Usually there a few different ways to do what you want and the commands themselves are not very easy to remember. So here is a list of some useful commands. I will continue to update it when I stumble upon something worth adding.

df -h
disk space usage

lsblk -f
list hard drives and mount points

mkfs.ext4 -L label /dev/sda1
create ext4 file system

rsync -r /source/ dest
copy directory or sync changes

iwconfig
configure a wirless network

nmcli
Network Manager

nmtui
text user interface for controlling Network Manager

paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
see system temperatures in human readable format

stress-ng --cpu 4 --cpu-method matrixprod --metrics-brief --perf -t 60
60 seconds cpu stress test on 4 cores

iftop -BP -i eth0 -o 40s
view network traffic sorted by 40s average