This is a tethered jailbreak. If your battery dies or you reboot, the iPhone will stick at the Apple logo. You must reboot the phone using a computer tool (like RedSn0w "Just boot") every single time.
rely on specific low-level vulnerabilities to bypass Apple's digital signature checks: iphone 4s custom ipsw
For a downgrade to iOS 6.1.3 (Untethered), use the by TheAnonymousM. This is a tethered jailbreak