How do I export my contacts as a .csv or .txt file?
You can do a search (of any kind) and the resulting screen will have an Actions select menu. Select any or all of your contacts and then you can select the Export Contacts in the Actions menu.  See https://docs.civicrm.org/user/en/4.6/common-workflows/exporting-your-contacts/

You can also run any number of reports and save the result as a CSV.