Dahlias are late summer flowering tubers and will be flowering or making buds about now,
They like added manure (animal if poss) to the soil where you want to grow them, this helps to feed the tubers and also retain some moisture around the roots, some people are lucky enough to be able to leave the tubers in the ground all year and just a 2/3 inch cover of compost / leaf-mold etc will keep them frost free for winter.
If you lift the tubers, it is best to cut off the stems about 2 inch from tuber, then turn tuber upside down to let all moisture run out from the stems (stems are hollow) as if you don't, the tubers will rot in storage, place them upside down like spiders walking across the newspaper, leave for several days in a cool place (garage, basement etc will be fine) once they have dried out at the stems, then I give a dressing of Flowers of Sulphur, this keeps all the viruses away that are prone to attack the tubers and cause mold etc. You buy this at the pharmacy here, a small bag will go a long way as how you cote the tubers with this powder is, get a largish paper bag, pour in the powder, add a tuber and gently shake tumble it about and this will coat the tuber.
After you have done this you either keep them in a cardboard box OPEN, and keep an eye on the tubers, keep a space between the tubers, any sign of rot etc, remove this like cutting an apple, then dust with the powder again.
Another way is to place the tubers into a box with slightly damp shop bought compost, gently bang the side of the box with hands to get the compost to settle between the tubers, keep an eye on them as before and next year soon as you find little green shoots
March / April, it is time to GENTLY lift from the box and pant out in the garden.
This is the time you can also take cuttings or cut the tubers into smaller bits with a good piece of root / tuber attached.
This year you wont get flowers on the dahlia's or the bulbs as they are out the ground BUT you should get a good show for next year with proper care. Hope this helps you out.
Good luck, WeeNel.
WeeNel has very good advice for storing. I'm not sure what zone you're in but here where I live, I plant my bulbs out in late November or December. That way they will come up when they are ready in the spring which, of course, is much earlier here than farther north. I have a bright orange dahlia and I just love it. They are such showy flowers. BTW, mine is 4 years old now and puts on more blooms every year. I have it planted where it gets only morning sun.