A token is a way to let others verify that the source of a piece of data is from you. First, select "Generate Token" from your Nxt Account:
Then insert any text, e.g. a URL or a message into the textfield and click 'Generate':
You will receive a string that looks like this:
q9m1plv0omr76rmu9ku72gvro.... This is the token produced from the text you entered and your private key. Since no one else knows your private key, only your account could have produced this token. By sending this token along with the text, the recipient can validate (via your public key) that this text must have come from someone with access to your account, i.e. you.
1 Byte Format
The authorization token has the following byte format:
32 bytes of public key + 4 byte timestamp from nxt epoch + 64 byte signature of the first two with the text of the token prepended to them in byte format.
- Alex Jones. . Retrieved on 11 June 2014.