Find an Image/texture. If you're using Google Images, make sure it's set to Large, so you shouldn't have too much trouble finding one with a good resolution. -save to desk top -no watermarks. Open illustrator. Set the document to 8.5 by 11 or "Letter size" Go to Window>workspace> and then click "default" or in CS4 it's called "essentials". Go to file, place. Find the image you saved to the desk top and click. Check the size. How much space does it take up on the art board? Illustrator tells no lies. If it doesn't extend far enough to the width of the page, it's usually advised that you should just find another picture. If it is too large, to size it down, use the black arrow key to select it, grab one of the corners, and MAKE SURE to hold down "option" and "shift" on your keyboard to make sure the dimensions are locked. People screw this up more than you know. That's why things look unintentionally stretched or too pixelated. Looking ok so far? Bonus points if you open Photoshop, open your picture, and adjust the brightness/contrast or add your own extra flare to the image via color or a filter. If you do this you will have to remember to re-save it as a png or jpeg to place it back into illustrator.
Now you're ready for your text!
Find a font. You can use one you already like on your computer or you can download a free one at websites like dafont.com. If you use this website, make sure you use the preview your text option, it just makes things go quicker. If you downloaded something from dafont.com, you need to make sure you open it up in the finder, and then open up (in applications) Font Book. Scooch the windows around so you can see both on your screen, and then click and drag the new font folder over to fontbook, under the "User" tab on the left. In illustrator, go up into "Type">font> and see if the name of your downloaded font is in the system. Over in the left hand tool bar, click the "T" for type, and use your mouse to make your text box. Select your font and type away. Adjust the font size as needed. The text should not exceed the rectangular area of your picture.
Time to make your clipping mask!
In the tool bar, click the black arrow button at the top left, and now click on your text to move it on top of the picture you have in your artbox. Make sure the text is still selected, (blue box around it) and click at the top Object>Create outlines and this turns your text into a vector. If "create outlines" is grayed out, (technical term!) then you may need to click on the black arrow button on the tool bar again, and make sure that your textbox is selected. Having that black arrow still selected, click on a white area in or around the document frame that is LEFT and ABOVE your picture with the text resting on it. Click and drag down and to the right, making a rectangle selection that includes all of your text as well as the picture. You did it right if you see that everything now has the blue selection box boarders after you've lifted your hand off the mouse. Now that everything is selected go to Object>clipping mask>make. If it worked you should see your text, but instead of it being black, it contains the texture from your photo, like the example shown.