It’s very easy to put on the goggles, and some straps are specially designed to make it easy for children to put the goggles on themselves. Anyway, you should hold the goggles in one hand and strap in the other. Stretch it, and put them on your child’s head, resting the goggles on their forehead.
If this model of kids goggles has two straps spread them apart at the back of the head for increased comfort. The lower one should be horizontal and the upper one should be separated a bit. Then you lower the goggles on their eyes, and adjust the straps further so your child is comfortable. That’s it, you’re ready to go!