i download a new font,all is as *.ttf
i want to know how can i install these fonts to the ubuntu？
please tell me the detail method to make it successful,
i'm a beginner!
thank you!

look in system settings and find something called Font Installer.it is in one of the opitons shown there. Run it and you will see a button saying add font; click on it, go to the folder where you have the fonts you want to install, sellect them and click on add font button on the lower right. it will take some time depending on how many fonts you selected, but in the end you,ll have your desired fonts installed.
PS: you might need administrator privileges on this action, i.e. to know the root (superuser) password, but I,m not sure

but there's no fonts function on ubuntu,
i can only set the font size on it.

I've been using Ubuntu for at least five months and I've still not found out how to install True Type Fonts. It's been bugging me for a while. I originally thought I'd search for *.TTF files and then copy the new fonts to that directory.

go to /usr/share/fonts
You should see folders for---eg truetype and type1. In the truetype folder will maybe be some subfolders. Put your ttf file in the appropriate folder.

I think it is that easy--note that an application will typically have to be re-started before seeing the new font.