How can i apply capital losses from previous years to this year's capital gain. I'm using Online version.

You must enter in the losses from previous year in order for these losses to be applied. 

In TurboTax Free:

1. Search for "Net" and the form "Net Capital Loss" should be listed.
2. On that form enter all the Net Capital Loss you incurred for the respective years.

These steps may similarly be repeated for "Non Capital Loss".

For some visuals, click on these screenshots: