The default LAN IP is 192.168.3.14 (so therefore ssh root@192.168.3.14)
PiFi must have been set up via the app so that an SSH password is set (admin password it’s called in the app)
The ethernet cable is default WAN so if cable connection from Pi to laptop (for example) that wouldn’t be right. Instead, you would connect to the wireless access point - e.g PiFi 4 Setup (default password RaspberryPi314 unless already personalized the access point in the app with your own SSID/Password on your device and then SSH)
Other ways to install packages is PiFi App > Settings > More Settings > LuCI > (LuCI > System > Software (update lists / then install whichever package you want)