Enable SSH and add WiFi to your Raspberry Pi (headless)

Connect your microSD card to a computer. Navigate to the boot folder.

SSH

Create a file with the name ssh. The file does not need any content.

WiFi

Create a file with the name wpa_supplicant.conf. Add the following content to the file:

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
country=BE

network={
	ssid="ssid"
	psk="password"
}

Now you can boot your Raspberry Pi. It will enable SSH and your Raspberry Pi will connect to the given wireless network.