How to mix textures?

Say if you have a road sign, that it’s a board with some painted texture, you want this to be
the base sign, and you want to put text on that
sign, that deffers from one to another, one way to
do it is to put the text on a separate polygon slightly offsets from the board’s surface, the other is to mix both the sign’s texture with the text’s one, how to accomplish this mix as a step by step?
Thanx alot.

You can use multitexture.

Look at glActiveTextureARB call.

Using a GL_MODULATE call on the second texture unit will work nicely for you although there are more advanced methods like the combiner and crossbar extensions and ultimately fragment shaders that get around the limitations of simple multitexture.

For now use basic multitexture.