This will be just a short explanation but I hope it will tell you what to look for.
There are two parts to your "problem":
1. browse, we use here the name "file dialog" and you can start by reading this
http://www.b4x.com/forum/basic4andr...android-views-controls-dialogs.html#post41804 and following the links to the library. It makes a difference if you know the directory in advance or want to browse the whole file system.
2. After selecting the file, you have the directory and the file name. You can set the image to the imageview by using this command- [imgviewname].SetBackgroundImage(loadbitmap(Dir,filename))
Of course the size of the imageview and the size of the bitmap may not be the same, and you have to fix it. If you set the imageview Gravity to Fill - the bitmap will be stretched or shrunk to fit the size, but the ratio of width and height will change, so you'll probably need to define a canvas and to draw the bitmap on the imageview, setting the size accordingly.