systemd is the init system on modern Linux distributions. It starts services at boot and keeps them running. Two commands cover most of what you'll do: systemctl and journalctl.

Managing a service

sudo systemctl start nginx
sudo systemctl stop nginx
sudo systemctl restart nginx
sudo systemctl reload nginx     # reload config without downtime
sudo systemctl status nginx     # is it running?

Start on boot

sudo systemctl enable nginx     # start automatically at boot
sudo systemctl disable nginx

Reading logs

journalctl -u nginx             # logs for one service
journalctl -u nginx -f          # follow live
journalctl -u nginx --since "1 hour ago"

Running your own app as a service

Create a unit file in /etc/systemd/system/myapp.service with an ExecStart line and Restart=always, then systemctl enable --now myapp. systemd will keep it running and restart it if it crashes — far more reliable than nohup or a screen session.