usepackage: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/usepackage - from package: usepackage

You may install the required package with command apt-get install {package}

Error in other languages:
usepackage: bevel nie gevind nie
usepackage: comandă negăsită
usepackage: comando não encontrado
usepackage: commande introuvable
usepackage: command not found
usepackage: käsku ei ole
usepackage: không tìm thấy lệnh
usepackage: komanda nerasta
usepackage: Kommando nicht gefunden.
usepackage: kommandot finns inte
usepackage: komut yok
usepackage: nie znaleziono polecenia
usepackage: níor aimsíodh an t-ordú
usepackage: no se encontró la orden
usepackage: no s'ha trobat l'ordre
usepackage: opdracht niet gevonden
usepackage: parancs nem található
usepackage: perintah tidak ditemukan
usepackage: príkaz nenájdený
usepackage: příkaz nenalezen
usepackage: команда не найдена
usepackage: командата не е открита
usepackage: 命令找不到
usepackage: コマンドが見つかりません