You should, in almost every case, add a new layer to put your text on. You can also go to layer properties and mess around with a few different options.
Something I made just because I was bored. It was just supposed to be some abstract piece of junk, but it came out looking like a couple of teardrops.
[i started with a black-non filled circle, on a white background.
I save all my work as a .pdn and a .png [.bmp on special occasion]
So that in case I need to add or edit something, I always have a .pdn file so you always knnow how you did everything. You might want to too