If you have a keyboard, you can hold down [Ctrl] while clicking on parts to select multiple. [Ctrl] and [Shift] also work in the Graph tab. Or you can hit ** to bring up box select. Or you can click on the [b]Selection Tools** [W] icon (top one on the left sidebar, looks like a mouse pointer) for more select options. This last one works even if you don't have a keyboard.

You may want to Group your parts now. Keyboard [J] or 6th icon from the top, looks like a folder with an arrow going in.

To clone your parts, you can hit [D] on the keyboard or use the Clone icon (4th from the top, looks like two 1x1 bricks).