For example if you want install this font downloaded from this website:
You should make a directory in your home, called .fonts (if it doesn't exist):
and then copy or move the file *.ttf, from the place where you have downloaded it (the ~/Downloads dir for example), in the directory just created.
The directory .fonts is hidden as you can see, because the first character is a dot, so you need anable your own file manager to see the hidden folders if you want install the font without command line.
cp ~/Downloads/Satisfaction.ttf ~/.fonts/Satisfaction.ttf
That's all, very easy isn't it?