As the title says. Can I make RingCT transactions now on mainnet. If so, how? What is the command or its options in simplewallet?
The fork is not quite here yet, there's a few hours left till it happens.
After the fork, up to date wallets will automatically generate RingCT transations if they detect the fork has happened. There is no particular setup to do, it's automatic. Pre-RingCT outputs will be used as necessary, and the outputs will be RingCT outputs, so as transactions happen, you will have less and less pre-RingCT outputs, and more and more ringCT outputs.