There are a number of free online survey tools on the market, but Google Forms and SurveyMonkey tend to stand out as most commonly used.
Google Forms is part of Google Documents - here are full written instructions about how to set up a survey in Google Forms.
SurveyMonkey is a free tool that allows you to develop a survey of up to 10 questions. If you want advanced features such as export of results, you have to pay a fee. This tool also requires you to set up an account. Instructions for using SurveyMoney can be found in the written tutorials.
Which is best?
The best advice I can give is that you have a play with each tool and decide which is best according to your own particular needs. I think it is easier to set up a survey in SurveyMonkey but I prefer Google Forms because it allows you to have more than 10 questions and exports results into a database ready for analysis.