an IRA (basically a CD right?)
No. IRA means Individual Retirement Account, and accounts are buckets.
Some companies (Fidelity, Vanguard, Charles Schwab, etc, etc) let you put almost anything in that bucket. Stocks, bonds, CDs, mutual funds, ETFs, even let it sit in "cash".
Other companies (read: banks) only let you put one type of thing (cash or CD) in a bucket.
Yet other companies let you put real estate in the bucket, and others allow you to put precious metals in your bucket at their firms.
Are they then going to offer me some kind of managed portfolio for the money in that account?
They'll offer, but you do not have to accept. I, for example, choose what stock and bond mutual funds and ETFs to put my money in.
If the money is going to be in flux then how is it secure for them?
It's a secure as the type of security you decide to invest your money in. If you're worried that that the IRA is going to become worthless, then don't put your IRA "eggs" in one basket named Enron. I, for example, diversify across a set of solid companies (Proctor & Gamble and Microsoft aren't going to stop making money hand over fist any time soon, and even if their stock values drop during a crash, they're still going to make money hand over fist, and investors will still want those stocks) using mutual funds.