[very basic coloring question]

Hey there, I'm Sam, new to this forum and new to Affinity Designer.

 

I make buttons as a hobby and used to make my designs with a different kind of software.

It didn't allow me to type on a path (very handy with buttons) so I switched to Affinity Designer, downloaded the

trial version this morning and I'm checking out all the basics.

 

Very basic question: I don't know how to fill spaces with a different color in jpegs I found on the net

and want to use for my buttons. For example: in the first attached file, I would like to change the white

background to a different color. I had a fill button in my other software, I used it to change the background

color to green (second attached file).

 

What am I doing wrong?

 

 

 

Thanks!

 

 

Sam