How do you make a call to the US from outside the US?

The country code for the US (including territories), Canada, and a smattering of islands in or near the Caribbean, is +1. The plus sign indicates "insert your international access prefix here"; different countries use a variety of prefixes, but '00' is the most common.

However, if you are in Canada, or on one of the 18 Caribbean-ish islands that are part of the North American Numbering Plan, you dial "one-plus," just like you do within the U.S.