Of course al that is possible. You should understand the pricipe of masks to see this is nog a big issue at all. There are tons of tutorials out there. You can attach a mask to a layer. That can be a pixel-based mask, or a vector-based one. For both it is the same: what is white will show the contents of the layer, what is black will hide, i.e. what is black, will turn transparent. Every greyscale between black and white will result in a gradation of transparancy. you can brush, paste or draw any shape you like. Masks are a biggie in Photoshop. They are also used in Adjustment Layers, on layer groups. Look around and discover a world of possibilities!