Browsing results
Columns, the inspector, and reading the numbers.
Columns, like Finder
Selecting a folder opens its contents in a new column to the right, so you can go as deep as you like and still see the path you took. The breadcrumb along the bottom scrolls to keep the deepest folder in view.
If you prefer a tree, Settings can switch the browser to an expandable table instead.
Reading the sizes
Sizes are colour ranked within each folder so the heavy items stand out without you reading every number. If you find it noisy, turn off Rainbow size colors in Settings and everything renders in one neutral colour.
The inspector
The info button opens a panel with the full path, both size measurements, file and folder counts, the modification date and the access state. It is only enabled when something is selected, because there is nothing to inspect otherwise.
Restricted folders
Folders macOS will not let DiskPeek read are still listed, marked with their own icon, so you can see they exist and that their size is missing from the total. That is deliberate. Hiding them would make the numbers quietly wrong.