I can see you like dogs so let's use a dog to show how these words are used. Your pet dog Spot has been very naughty, chewed up your tv remote control, but in the evening you decide to OVERLOOK his behaviour and give him some supper anyway. But when he jumps up and asks for more, after supper, you IGNORE him and carry on cooking your own food. He has had enough to eat, although Spot thinks that you are NEGLECTING him.
Overlook is usually used when someone ignores something bad.
Ignore is the same as pretending that something (or someone) isn't there.
Neglect is not giving someone or something the attention(time, food) they need.