Lettering

Hmm... There are different techniques you could use and experiment with, but I think this is would be the easiest:

Go to the text tool, and look over to the bottom right and find the fill textures.
http://i.imgur.com/Kw0Xk7Q.png

There are two textures that come with the program, wood and cloudy. You can change the colors of them by clicking the two colored rectangle buttons above the number boxes. Experiment with the numbers, and try to find a configuration you like.
http://i.imgur.com/KcjQGI9.png

You can add in details like cracks and moss in this step. After you are done touching up the texture, go to the bevel tool located at the top toolbar.
http://i.imgur.com/iYe3L67.png

You can look at the different bevel styles and change them to your liking.
http://i.imgur.com/pOLzXDh.png

Optionally, you can give more dimension to the stone text by copying the image you have and then pasting a copy on a layer underneath the current one. Move it just a little bit and then go to the brightness tool and pull the lever all the way to the left to make it black. You can then take a black paint brush and touch up anywhere it looks odd.
http://i.imgur.com/SANUcXy.png

The finished product:
http://i.imgur.com/dXtnuSM.png

I hope this helps you.
Good luck! 😊