you can most likely use the magic wand tool for pikachu, just use the magic wand tool and click anywhere in the white background behind pikachu then just erase everything,
but for other stocks you will have to use the pen tool to make a cut around pikachu... make sure the pen tool is set to paths, then right click and choose make selection, hit ctrl c; ctrl v
to make a border, I find the best way is to make a new layer after your piece is finished, and go to image> apply image, hit ok.
ctrl + a; ctrl + c; ctrl + d; ctrl + n
now you need to know how to count...
you will be making a new document... if you want a simple 1 px black border, increase the image size by 2 pixels wide, and 2 pixels high
make the background black and then hit ctrl + v
if you want a bigger border, use more pixels, for example if you want a 5 px border and your image is 370x120, make the new document 380x130
it's a lot more simple than it sounds, and outcome is good.