HyperCard text is contained in fields, which you create or modify using the Field tool. You edit text in the fields when the Browse tool pointer is an I-beam
(whenever you're over text that can be edited). You set properties for the selected field by choosing Text Style from the Edit menu or typing Command-T. A text field can be on the card or in the background.
Each card can have a card picture as well as a background picture it shares with other cards.
You use the Paint tools and the commands in the Paint, Options, Patterns, and Edit menus to edit either the card or background picture.