I have Movie Studio 2023 Platinum and a first time user. I added a rectangle template mask to a video but need to alter its dimensions and reposition in the frame. I can't see how to do this.
@RobStirl click on the mask on the timeline highlighting it yellow, then click on Size/Position/Rotation in the Effects tab, you'll then have controls to reshape the mask.
PS. you can change the Alpha of a mask with the little up/down arrow at the start of a clip, also some masks are B/W & some are W/B, you can change the background by right clicking - Background Design.
In addition to @Former user's example see the tutorial list here for tutorials on 'how to's' you may find useful - though some are done in an older version of Movie Studio (previously called Movie Edit Pro) the principles are the same..