We don't have an online tutorial of using Primatte Studio from within the Vegas host at this time but we'll make one. Essentially, you need to use the sample tool to make that happen. Set the Sample Point control in the area of green / blue screen of the clip that you wish to sample, then select the desired sample shape (single point, 5x5 array or 50x50 array) and then click the Take Sample button. You can then move the Sample Point to another place in the image to add to or subtract from the sample.
From there you can follow the directions included in the included documentation to complete the job of removing the green / blue screen.