Answer:
You don't physically enter the + sign. The + is the internationally recognised way of listing a telephone number in a foreign country. The + means that you dial whichever is the code to access international from your own country and then that country's national code and then the number that you want. '00' is used in most countries to access international dialling. So, for example, if you wanted to call London. England from most other countries, you would dial 00 44 20 xxxx xxxx
Be aware that calling international on a mobile (cell) phone can be very expensive.