Step 6: Solder the Cathodes of Each Row Together
Solder the cathodes of each of the five rows together. The cathode is the short or negative end of the LED. You will end up with 5 rows of cathodes that are all tied together. For now, do nothing with the anodes.
Some of the cathodes will be too far apart to solder together. Simply cut and strip some jumper wire for those stretches. Make a small hook on the end of the wire and the LED lead, then squeeze gently. This should make it relatively easy to solder the jumpers in.