Well for a smAsh (single malt and single hop) extract beer, you'd obviously use pale extract as your base. And FWIW, a 6-7% abv IPA puts you more in the camp of AIPA, not IIPA - not a bad thing (to me), as IIPA can be tricky to drink 5 gallons of while the hoppiness is at its fresh peak. IIPA is generally 7.5-8% + abv. So here are some guidelines:
1. Malt - 8 lbs of pale DME (dry malt extract) preferably OR 9 lbs of LME (liquid malt extract) in a 5 gallon post boil batch would put you in the 1.065(ish) OG range, which loosely correlates to a 6-6.7% abv IPA. And actually, to get better attenuation it's a good idea to substitute maybe 1/2 lb table sugar for 1/2 lb DME (ie., use 7.5 lbs DME, 1/2 lb sugar). I also recommend Briess DME as it is more highly fermentable than most other extracts.
2. Hops - Centennial is a great hop to use for your first IPA as well as a single hop IPA. It's citrusy and slightly piney, and can actually function as a bittering hop and late hop.
I'd use: 1.25-1.5 oz for 60 minutes
2 oz each @ 15, 10, 5, and 0 minutes left.
Dry hop with 4 oz more in a hop bag for a week @ room temp after fermentation visibly ends.
3. Yeast - Wyeast 1056, White Labs 001 or Fermentis US-05 dry yeast.
This is a good start. As you brew more, there are tons of other great hop varieties and hopping techniques to check out, but this will make a good beer. Good luck and welcome !
EDIT - Since the extract manufacturer made the extract to their specs using various water salts/additions, I'd use either reverse osmosis or distilled water, which are very low in these compounds.