You need to go to Design -> Themes -> Select your current theme.
Once there go to the "Sections" tab on the top left, select the section of the website you want to add the widget too. Once the section is hightlighted you will see a "Add New Widget To {Section Name}", click on that and select "Text Field". One you do that it will open up the settings of that widget, simply fill those out and click on "add" to save it.
