Depending on where you're staying, your hotel may have a small water slide for you to get started on - try the one at your hotel if it has one first.
Next, at TL, you'd want to try the storm slides - this is probably your best bet to be introduced to water slides. They are twisty slides, without any big drops - these are my DH's favorite slides, and we spend most of our time at TL on these slides.
You may also want to try Crush "N" Gusher at TL - a water roller coaster, though everyone says "keep your butt up" (something about the rollers they use to propel you up hills, I think).
TL and BB both have some nice inner tube slides too - family, one or two person slides - those tend to be less twisty and less fast than a body slide, so you may want to give those a try as well.
If you like roller coasters, and you SCUBA dive, you should really like most water slides - just start small (with the storm slides), and work your way up!