If you haven't played the original, yes it's an RTS like C&C. It involves 3 different races:
Zerg: Mutations basically
Protoss: "Futuristic" race
You can download a free trial from battle.net I believe and can play in offline mode as Terran only versus computer. I would check that out first before you buy it. It's been dropping in price some, I think it's between $30 - $35 right now.
Learning curve is different from playing against computers and people obviously. Terran would be the easier to start with (since it's what you play as in the single player campaign). There is a learning curve for any of them, if you haven't played before.
You build structures, each one able to produce units or equipment upgrades. Three different tier levels, etc. If you've played C&C you'll have some grasp to it.
It's fun, addicting and all around good game