Using a Raspberry Pi as a Wireless Access Point
The official Raspberry Pi documentation contains a tutorial for setting up a Raspberry Pi as a wireless access point using hostapd: https://www.raspberrypi.org/documentation/configuration/wireless/access-point.md.
The Edimax EW-7811Un is a wireless dongle that supports both wireless client mode and access point mode. To set up this dongle for access point mode, older and newer tutorials suggest to patch the wireless driver as well as hostapd. Even until recently, issues with getting that Edimax dongle to work in access point mode have been reported.
Fortunately, it turns out that the official Raspberry Pi images have been supporting the Edimax EW-7811Un dongle out of the box for a couple of years without patching any drivers or hostapd. To get it working, set driver=nl80211 in hostapd.conf.