You can first practice using a Pi Camera:

Getting started with the Camera Module.

Then, connect a button to the Raspberry Pi GPIO. See the image below.

Here is an example of the python code that takes a picture each time you press the button and stops when you press "Ctrl C":

from picamera import PiCamera

from time import sleep

from gpiozero import Button

button = Button(17)

camera = PiCamera()

camera.resolution = (1920,1080)

camera.start_preview(alpha = 200)

frame = 1

while True:

try:

button.wait_for_press()

camera.capture('/home/pi/Desktop/frame%03d.jpg' % frame)

frame += 1

except KeyboardInterrupt:

camera.stop_preview()

break