Most engineers use a 5G phone every day. Almost none can explain what happens in the first 2 seconds of connection. 
Here’s the complete 9-step flow — explained simply.
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Every time your phone connects to a 5G network, this happens 
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① Cell Search & Synchronization Your phone scans for the nearest gNB. It reads the SSB — Synchronization Signal Block. PSS + SSS + PBCH. Timing acquired. Network found.
② Random Access (RACH) Phone knocks on the network’s door. 4 messages: Preamble → RAR → RRC Request → RRC Setup. Connection attempt begins.
③ RRC Connection Setup Radio link established between UE and gNB. Defined in 3GPP TS 38.331. Your phone now has a radio channel. But no identity yet.
④ Registration Request Phone sends its identity to the AMF via gNB. NAS Registration Request over N2 interface. Network asks: who are you?
⑤ Authentication & Security AUSF and UDM verify your SIM identity. 5G-AKA protocol. SUCI → SUPI verification. Subscriber confirmed. You are who you say you are.
⑥ Security Mode Setup Encryption keys derived and activated. K_AMF → K_gNB → K_RRCenc / K_UPenc. Everything from here is encrypted end-to-end.
⑦ PDU Session Establishment Phone requests a data session. AMF → SMF → N4 → UPF. User plane path created through the network.
⑧ IP Address Allocation UPF assigns your phone an IP address. 192.168.x.x → N6 interface → Data Network. Your phone now has an address on the internet.
⑨ Session Active → Data Communication Internet. Video. VoIP. Apps. Everything flows through UPF → DN → your screen. Total time: under 100ms. 
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The 5 Network Functions making this happen 
AMF → Your identity manager. N1 + N2 interfaces.
AUSF/UDM → Your authentication engine. N12 + N8 interfaces.
SMF → Your session controller. N11 + N4 interfaces.
UPF → Your data anchor. N3 + N6 interfaces.
PCF → Your policy enforcer. N7 interface to SMF.
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The interfaces that connect them all 
Uu = UE ↔ gNB (air interface) N1 = UE ↔ AMF (NAS signalling) N2 = gNB ↔ AMF (control plane) N3 = gNB ↔ UPF (user plane) N4 = SMF ↔ UPF (session rules) N6 = UPF ↔ Internet (data out) N7 = SMF ↔ PCF (policy) N11 = AMF ↔ SMF (session setup) N12 = AMF ↔ AUSF (authentication)
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The next time someone asks you what 5G is —
Don’t say “faster internet.”
Say: a 9-step cryptographically secured service-based architecture that connects your device to a distributed cloud-native core network in under 100 milliseconds.
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And if THEY want to understand it too — send them this post.