Tempura is basically deep-fried whatever-you-like. You can have seafood tempura, or vegetarian tempura, or, hey, fruit salad tempura if you're feeling goofy. (If you make the latter, let me know how it turned out. I
don't think I'll try it myself.) The main requirements here are batter, stuff to put in the batter, hot oil (I use canola), and a desire to make a mess in your kitchen.
What you'll need:
A box of tempura batter
for frying, deep enough to immerse the items to
Items to fry: imitation crab meat,
popcorn shrimp, jumbo shrimp, squid, sliced salad mushrooms, shiitake
mushrooms, slices of sweet potato, baby carrots,
broccoli, and whatever else strikes your fancy.
You can make your own tempura batter if you're feeling ambitious, but I just use a mix from the grocery store. I set some of the mix aside, however, to roll the stuff to be fried in. This pre-coating makes the batter stick much better. I also use Panko,
breadcrumbs made especially for tempura, which add a nice crunch.
So, get you some stuff to cook.
Slice it thin enough that the oil can cover it. Big
broccoli florets and whole mushrooms will be a problem
unless you have a deep fryer. If you have raw shrimp, peel and devein them (info here if you need it) and leave the tails on so you can hold them by the tails during preparation. Heat
the oil to between 320 and 350 degrees F; I highly recommend
you get a candy/deep-fry thermometer to keep the temperature
from going too high. For everything but the shrimp-with-tails,
stick it on the end of a bamboo skewer, roll it in the dry batter until covered, roll it in the mixed batter until covered, roll it in the breadcrumbs (if you have 'em) until covered, and then push it off the skewer and into the oil with a fork. Repeat like an assembly-line machine, taking items out as they cook through and draining them on a plate covered with paper towels. Each item should cook up in just a few minutes. Breadcrumbs will turn golden brown; if you have batter only it won't get that dark, so don't
wait for it or it'll be overcooked.
Serve with tempura dipping sauce. As with the better, you can Google up a recipe, or you can just buy some at an Asian market. I like the Kikkoman brand. I have some little sauce bottles made to fit into bento boxes for this.