You can kill a process by:

knowing process name

pkill process-name

or

ps au | grep process-name
kill process-id

clicking on process window

xkill

knowing a port number that is blocked by the process

using npm cli tool

npx cross-port-killer 4321

using lsof utility

kill $(lsof -t -i:4321)

or more fancy way with fzf and unix fu

portkill() {
  local pid
  # get processes listening on local numbered ports and output process id, port number and process name
  pid=$( \
    netstat -tnlp 2>/dev/null \
    | awk 'BEGIN { OFS = "\t"; print "PID","PORT","NAME" } $4 ~ "(127.0.0.1\|\[::\]\|0.0.0.0):[0-9]" && $7!="-" { gsub(/:::/,":"); split($7,a,"/"); split($4,b,":"); print a[1],b[2],a[2] }' 2>/dev/null \
    | sort -n -k2 \
    | fzf \
    | awk '{ print $1 }' \
    )

  if [ "x$pid" != "x" ]; then
    echo $pid | xargs kill -${1:-9}
    echo "Process $pid was killed"
  else
    echo "No process was killed"
  fi
}