The white border is the background of the jpg heart.
Since you are beginning, I don't want to explode your brain into deep space immediately by trying to post something too complex.
So, try this quick way first. If the image has 2 colors, white bg and red heart, this should work okay.
Menu: Select...by color. Click on the white background. Menu: Select...grow. Grow selection by 1px, click OK. Hit delete.
OR
1. Download transparent heart to your images folder. Google "heart png" and pick your favorite.
2. In Gimp. File: New, image width 1920, height 1080. (for a FullHD canvas)
3. Open the heart, select all and copy to clipboard. (ctrl + a, ctrl + c)
4, Switch to empty canvas. Menu: Edit/paste../as new layer.
5. Duplicate the heart (ctrl + shift + d or from menu: Layer/duplicate layer). Begin to manipulate the copy.
PS. If you don't know anything about image editing, I would advise to go through some basics first.
Like the wikipedia page for example, there's lot of 101 sites too.
https://en.wikipedia.org/wiki/Image_editingWill make things much easier in future.