Eagle prints everything you see on the monitor. To print just one layer you must disable the second (or any other)
To print the top (layer1) you disable the solder side (layer16) and the components (layer21). If you don't want to have the dimension (board outline) printed you must also disable the dimension layer (layer20).
Printing transparencies it is advisable to print the solder layer (16) the way it is. Mirror the component layer (in the print setup) to put it upside down on the PCB for exposure. That way the ink will be in direct contact with the board to prevent exposure caused by refraction.
To select or deselect a certain layer go to top left. Underneath the "I"nformation button there are three overlapping squares - blue, red and green. Hit that button and the numbers of the layers are displayed in a pop down window on the left. Active layers are marked blue. To uncheck, simply click on the blue rectangle and it will turn to white, meaning deselected. The result will be visible on screen right away.
If you have made the board after a schematic all connections are displayed as air wires. You can have the autoroute do the job or route manually.
Routing manually and changing layers for one trace just change the layer. Don't let go the trace you've already started. Change the layer and continue routing. Eagle will insert a via (solder pad without any part connection) automatically. A standard via is square shaped and requires a lot of space therefore. Change it to the shape you want, preferrably octagon. After the change all following vias will be octagons, too. To avoid the change just click 'via" before you start routing. Select the shape, diameter and drill. Starting to route the preselected type of via will be used.
I think you are asking how the current passes from the top to the bottom of the board.
If the board was made by a board house they would plate metal into the holes, but that is not possible with DIY so we solder in wires. The wire just goes from the top of the via hole to the bottom of the same hole.
I'm afraid your approach is wrong. You must not make the PCI-connections on the board. Instead you must apply the appropriate library. If you are using Eagle v. 4.16 you'll find a library <con-pc.lbr> There is a selection of PCI-connectors displayed in a preview window. There are three main types: PCI SLOT, PCI BOARD SHORT and PCI BOARD LONG.
Use one of those suiting your needs in your schematic. Make the appropriate net connections and type <board;>. The used parts including the PCI connector are then displayed on screen with air wires indicating the connection. Use the autorouter for initial routing. Eagle connects between top and bottom layer automatically using vias where necessary.
If you don't like the result just type <ripup;> and acknowledge.
your style takes a lot of guess work. So I guess the 'tow' layer is supposed to be the top layer.
When the board is etched like a single sided board you will have to use mechanical means for the vias as well as for solderpads conneced to the top layer. If it's a pure via you can make the connection from top to bottom with a thin piece of wire. Solder the wire to both layers and the via is done. Clip excessive wire after soldering.
If any connected part requires connection from top to bottom you must use the pin of the device the same way as with vias.
There are copper and silver rivets on the market which have to be inserted in the drill hole and either be pressed for contact on both sides or also soldered before placing a part. The rivets are hollow and after they are soldered properly you insert the part and solder like you do using a single sided board.
Using rivets you have to remember to drill according to the diameter of the rivet. For a part with a pin diameter of 0.8mm the rivet has a diameter of 1.0mm. You must be very accurate (0.1mm) and careful not drill away the pad.
A better and reliable way to make a double sided board is electrochemical. The copper is added to the board material after it is activated. PCB manufacturers use that method.
i have add PCI interface on my schematic but ther is wire conect together and don't show but at board connect and make routate more diffecault
i want to remove this wire but i can't because some ic connect to because its gnd or 5v
more than 10 5v and more than 10 gnd have at pci interface
i want to use only 1 each one
so i want to remove it from schematic to don't appare at board and dont attach with ic