You can use pass-in fields, as Bahadir mentioned, or you can use merged fields. Pass-in fields are used to append a value for a variable as part of the linke, i.e. gender=1, so it's kind of pre-answering a question when the person starts the survey.
Merged fields are similar, but they are tied to a password. For example, if you knew I was going to take your survey using the password 1234, you could set up some merged fields to populate things like FirstName=Brian, Gender=2, and so forth. When I type in 1234 to start the survey, those variables are automatically populated according to the merged fields you have set up.
For short video on creating links that have passwords and pass-in fields in them, please see https://www.sawtoothsoftware.com/support/issues/ssiweb/help_movies/pass_in_info.htm.
To read a bit more about passwords versus pass-in fields versus merged fields, you can read the help files in SSI Web or online at www.sawtoothsoftware.com/support/issues/ssiweb/online_help/hid_web_passwords_intro.htm