Network interfaces

eth0 is the interface that shows up when you plug an USB to ethernet adapter. A list of compatible ones is located here.
wlan0 is the embedded Wi-fi interface.
wlan1 (or wlan2, wlan3 etc.) is the name of a Wi-fi dongle.
usb0 should be the small USB port (not sure, may be the first plugged).
usb1 should be the big USB port (not sure).

Anyway, you can check the physical link connectivity, as root:

ethtool usb0
ethtool usb1
ethtool eth0

If you connect an OP with another using an USB cable, the OP at the little end of the cable will dramatically drain the current from the other OP's big USB port.
To avoid this, at the little end, type as root:

echo 0 > /sys/class/power_supply/twl4030_usb/enable

rmmod g-cdc

modprobe g_cdc

into

#modprobe g_cdc

There's also a bluetooth interface, but until now i just connected a mouse, so can't tell much about it.
These interface numbers (eth0, eth1 etc.) may vary, depending which one you plug first.
The numbers can be fixed using the /etc/udev/rules.d/70-persistent-net.rules file.
This file is deleted at each shutdown. To make use of it, edit /etc/rc.d/rc.local_shutdown , and comment this line:

rm /etc/udev/rules.d/70-persistent-net.rules

into

#rm /etc/udev/rules.d/70-persistent-net.rules

SL4P default setup

The Network Manager, well, manages the connections, and asks for an IP address through a DHCP request. This is how it acts when you boot SL4P for the first time.
You can set it up through a right-click on the NM-applet Xfce desktop icon (two little screens at bottom-right).
Although it's shipped in the Slackware ARM release, i grabbed and compiled a more recent version.

Wicd is included in the stock Slackware ARM extra packages.
I don't include it anymore inside 14.0 but you still can install it, using slackpkg or any other method.
I tried it only a bit so i can't recommend it, or not.
If you want to give it a try, be root, then install it, and disable the network manager:

chmod -x /etc/rc.d/rc.networkmanager

chmod +x /etc/rc.d/rc.wicd

Activate Wicd frontend under Xfce. Go in the menu -> Settings -> Session and Startup -> Application Autostart tab, then check "Wicd Network Manager Tray".
Reboot.

Historically speaking, stock Slackware doesn't use the Network Manager, nor Wicd. The network is established at boot, once for all.
If you want a non-graphical server-oriented setup, you have to disable the network manager (or Wicd).

chmod -x /etc/rc.d/rc.networkmanager

or

chmod -x /etc/rc.d/rc.wicd

netconfig

darkstar

otherwise you'll break some Pandora scripts compatibility. Sudo won't launch anything with the wrong hostname.

Set you parameters.
Eventually edit /etc/rc.d/rc.inet1.conf to finalize your setup.
Be sure to have all used interfaces plugged in when booting. With the deactivation of the network manager, it's no more plug and play.
Reboot.