In Scribus you can change the properties in several ways:
Using defined text styles
Using local modifications on the selected text with the text tab of the PP (F2)
The overall frame content when the frame itself, and not the content, is selected
The third option is very practical to work very quickly on a small document, but it is certainly not the most productive in all use cases. The best workflow will be to apply paragraph styles, then apply character styles, and then local formatting. In this chapter you'll see all the advantages you can get by using styles.
In fact the third method can sometimes put your work in great danger. Think of you having set everything nicely. You do one or two changes on other frames and want to come back on this one that you had already set. You will have to double-click on that frame to go into the Content Edit mode and do the changes. But what if double-click doesn't work well? The content will not be selected, but the frame...