Can't help with second question, spring means its a spiral bulb and tubes mean its long tubes that go up and down. Like normal household energy saving bulbs
5u and 8u means the bulbs are made of u shaped tubes grouped 5u has five u shaped tubes grouped in a circle look up 150watt cfl to see mogul socket is just the size socket needed for the bulb
oh and check the lumen rating on some smaller cfls you may get better light with a few small ones. 13watt are tiny and have a high lumen to watt ratio. getting 3 Y splitters and pluging 4 smaller ones into that socket may be way better, but i don't know what your setup is so may not work for you
Spring is the spiral twirly kind cfls, the look lke a spring ya kno? Mogul is just a bigger size socket than regular(standard) sockets that are in ur home. Mogul is also the size u need for a hps bulb, but hps bulbs don't work and are dangerous without a ballast.