I'm trying to use an LM324 op-amp in a schematic, but the parts I see in Eagle don't have the supply lines with the schematic symbol. For example, see the attached schematic. When I do the board layout, how do I connect the supply lines with the op-amp?
If you make an error check (menu: Tools->Erc) you'll see the net names of the power lines that aren't connected. For the LM324 they should be named V+ and V-
ERROR: Sheet 1/1: no SUPPLY for implicit POWER Pin IC2P V+
ERROR: Sheet 1/1: no SUPPLY for implicit POWER Pin IC2P V-
Then you have two options. Either use power symbols of the same name connected to your supply lines or just rename the nets to what's needed. Attaching a power symbol to a line will rename it for you. You can only have one name on a net, so you cannot call it V+ and
Vcc, so if you're using an LM324 together with eg. a 4093 (which has Vdd as its positive power line), you have to cheat a bit (or change the library to show the power lines, so that you can connect them to any named net).
For clarity, I use the symbols on schematics that other people should be able to read, but when I want to make a quick PCB for a proto, I just change the net names.