I have loaded Ubuntu 15.10 on a Dell Latitude D630. I have downloaded Gnome 15.10 and don't know how to load it. I have located it in the Ubuntu Software Center, and selected install, and booted the laptop, but after it restarted I can't locate it. Please help.

You should report your post and ask it to be created as a new thread -- it doesn't belong here.
That said a quick tip for you is that you do not download and install Gnome and waht you likely have downloaded is Ubuntu Gnome edition. So, you woujld either install Ubuntu Gnome Edition instead of Ubuntu or you would install Gnome within Ubuntu. The process would go something like this.

In general you do not manually download and install any software when using a distribution like Ubuntu but use the "Software Center" or package manager, in this case apt, to do so for you. This gives you some ideas of how to do it.

I went to the link you suggested and tried to do what it said, but when I got to the TTY1 screen it asked for Login and Password, but nothing I tried worked. Where does that login and password come from?

This should only ask you for a password which is the password for your account and the password will not be displayed as you type it. That is assuming you are using the account which you created when you installed Ubuntu. It shouldn't ask you for a username.

Where do I type this code? Any Terminal?

Exactly.

You can either open the terminal while in the desktop environment, by searching for terminal and opening the first one you see, and type the "code" (it's just running an install program with parameters) there or you can press Ctrl+Alt+F1, login with your usual username and password and run the command there then press Ctrl+Alt+F7 to return to your desktop.
Once Gnome is installed you can then log into the Gnome desktop by logging out of your usual desktop (Unity) then clicking the Ubuntu symbol on the login box and selecting one of the Gnome options from there.