today I tried out LyX and I have to say that I am a little frustrated. But I hope it's because I don't know enough yet and You can bring light in the dark

I wrote a little text with a title, some sections and subsections. When I checked the pdf-output I found, that the whole document was set in serif (like I wanted it to be), but the section-titles were set in sans. So I went back to the document and tried to change the ont family manual by right-klicking on the section-title and choosing user defined style. There I chose sans-serif. But this did not help, though in the document the section-title looked right: a little bigger, bold and serif.
Has anybody any hints for me?
Thanks in advance
Sven