Do I have to apply a capital loss from previous years to 2018 gains if it's included in my carry forward information or will Turbo tax do that for me ?

The loss amount will carry forward for you but you'll have to apply the chosen amount of the loss yourself in the Losses section.

Using the Find button, search and select the option "Losses" to apply the loss.

I have more Capital Gains Loss carry forward, than I have Capital Gains this year. But TurboTax seems to just let me enter any amount into the amount applied to this year on the LOSS WS. Shouldn't it only let me apply up to the maximum gain for this year?

Yes you choose the amount you want to apply against your gain. The unused amount will be carried forward for future years.