From charlesreid1

Making a Raspberry Pi a hotspot

See https://www.raspberrypi.org/documentation/configuration/wireless/access-point.md

Installing Stuff

sudo apt install dnsmasq hostapd dhcpcd5

Edit dhcpcd config file

Edit /etc/dhcpcd.conf and modify it to contain this:

interface wlan0
    static ip_address=192.168.4.1/24
    nohook wpa_supplicant

replace wlan0 with whatever interface you want to use.

Restart dhcpcd service

sudo service dhcpcd restart

Edit dnsmmasq config file

Edit the dnsmasq config file /etc/dnsmasq.conf, which determines what range of ip addresses will be handed out and for how long. Modify it to contain this:

interface=wlan0
dhcp-range=192.168.4.2,192.168.4.20,255.255.255.0,24h

This will hand out IPs starting at 192.168.4.2 and ending at 192.168.4.20, lasting for 24 hours lease time.

Modify wlan0 to whatever interface you are using to provide the wifi network.

Restart dnsmasq service

sudo systemctl reload dnsmasq