APs, SSIDs and controllers
An access point (AP) bridges wireless clients onto the wired LAN. An SSID is the network name clients see; a BSSID is the AP radio's MAC. In larger networks a wireless LAN controller (WLC) manages many lightweight APs centrally - pushing config, tuning radios and handling fast roaming.
Bands and channels
2.4 GHz reaches far and penetrates walls but is crowded and slow, with only three non-overlapping channels (1, 6, 11). 5 GHz has many more non-overlapping channels and higher speed but shorter range. 6 GHz (Wi-Fi 6E) adds even more clean spectrum. Overlapping channels on nearby APs cause interference and retransmits.
Coverage vs capacity
Turning AP power to maximum seems helpful but creates co-channel interference and sticky clients that won't roam. Good design uses more APs at lower power with a planned channel layout - a survey/heatmap confirms coverage without overlap. Capacity (many users) needs more APs; coverage (few users, big area) needs fewer.
Security and common failures
Use WPA3 (or WPA2 where WPA3 isn't supported); never WEP. PSK (a shared password) suits homes; enterprise (802.1X/RADIUS) gives per-user logins. Typical faults: wrong PSK (auth fails), DHCP not reaching the wireless VLAN (associates but no IP), RF interference or an overloaded AP (slow/drops), and a guest SSID mapped to the wrong VLAN (reaches the internal LAN).