Which footprint to use for LM324 SO-14 in KiCad?
A main concept of KiCAD is the separation of symbols from footprints. There is no LM324-specific footprint; you have to pick the correct one. Some devices (usually ones which have exactly one footprint, or one category of footprint) have footprint filters added to them; all the others do not. 

In the case of the LM324, this device is available in eight different packages from the manufacturer, spread across several categories, so it makes sense to let the designer pick the appropriate footprint.

In the schematic editor:


Make sure you are using all of the correct "gates" of this chip. That is unit A, B, C, D, and E (the power pins), all of one device such as U1. Make corrections if it tries to rename any of them, such as mistakenly naming the power pins as U2E. 
Click the "Assign PCB footprints to schematic symbols" button. Assign the "Package_SO:SOIC-14_3.9x8.7mm_P1.27mm" footprint to U1.
Click the "Generate Netlist" button. This saves a file with a text representation of all the connections present in the schematic. Of course, there must be wires or connections made for this to do anything.
Close EEschema, open PCBnew, click the "Load Netlist" button.  There should be no errors reported. Click "Update PCB" and place the parts.
"Rat's nest" wires should now be visible. 


This should look like the following on version 5.1.5-1: