In the right sidebar you will find the properties for the element you have selected. Which options you have depends on the element type. For example, with a label, you have various options for manipulating the text. Size, color, orientation - all these can be set here.
With a rectangle these are of course completely different characteristics. In the sidebar on the right you will find information about the fill color, the color of the frame, and so on.
For all visible elements, you can use the “Geometry” tab in the right sidebar to specify the size of the element, its position and auto resizing.