Probably by the question I'm going to make, you can see that I'm just stupid and understand 0 of this. But I want to make those clicker games and I'm not sure what I should use, Portrait, Landscape or the default project. And what "window size", because phone to phone it can change or I'm just being stupid?
I've made 3 games so far and from what I understand,
Portrait locks the view of the game to vertical (Holding your phone with one hand right side up)
Landscape locks the view of the game to horizontal (Holding your phone on a side. ex. watching a video)
Default lets the player orient their device the way they want (It may result in black bars appearing if the game was built for portrait, but played in landscape or vice versa)
95% of modern phones and tablets have the same aspect ratio (16:9) and the resolution is dynamically changed to accommodate the screen's resolution (ex. If you built a game designed for 1920x1080px resolution and played it on a 1280x720px res device, because these resolutions have the same aspect ratio, the game will be "automagically" scaled to 720p and the same goes for higher res devices, only the game will be stretched)
There are some devices that don't fit in this aspect ratio (like the apple iPad) If you are building the game for these devices you'll probably have to change some UI elements based on what device it's running on and it's a bit more difficult... (I'd just stick with black bars around the screen =D )
You can use this site to check what aspect ratio is a certain resolution: http://andrew.hedges.name/experiments/aspect_ratio/
Hope this at least somewhat helps,
Good luck with your projects!