Hi,

First, please allow me to remind you that installing .debs directly is not recommended. You do not know what the source is, and as a general rule, installing a .deb is like running an unknown executable on Windows; only do it when you trust the source.

That being said, you can open the X-Terminal, and type:

dpkg -i <filename>.

For example:

dpkg -i /home/user/Downloads/example.deb

Hope this helps,