Elevation Mars (U.S. $2.99) is a beautiful science-based app that will let you tour high resolution imagery of the 4th planet from our Sun and explore it in ways that simply can't be done from a book.
The app starts with a topographic map of Mars, and you can gesture to zoom, rotate and tilt the map. There are several options for viewing the base map, including actual NASA/JPL satellite images, then you can see layers with different colors for different elevations, and you can terraform Mars to see what would happen if there were oceans or water, which there likely were in the past.
The app features tours of 80 different Martian features, and there is a clever exaggeration slider that let's you see the topography in extended views.
Using the app is easy enough, but there is plenty of help built-in. Start with a base map and explore. Start a tour or look at any of the more than 1000 features that are visible, and read about them on the linked Wikipedia articles.