When creating a custom field you have three options, two of which create a text field: Text and Textarea.
Text. This is the default field type, and selecting this option creates a simple text box with one horizontal line and no controls. This option is useful if the value is expected to be a word or number.
Textarea. This option is available from the dropdown menu, and it specifies an input box that supports line breaks. This type of field can be expanded both horizontally and vertically using the handle in the lower right corner.
Note: The third field type is Select, which allows you to create a drop down list instead of a text box.