Got a newbie question

I've seen this effect on tons of websites and can't for the life of me figure out how to do it. Can someone tell me how to make this effect?



(PS. I'm talking about the dot pattern thing.)

okey there are 2 layers there...
First the background that gray thingy and then the dotted pattern on it...
So here is what you should do..
Make a new window...and make the size of it maybe 6*6 big...
Then just make a dot in the upper corner left corner...then delete the background so it's only that dot you have there...
Then go to edit -> define pattern...name it...
And Tadaaa!There you have it...
Now just choose where you want the pattern and take edit -> fill -> pattern...
Hope this helped :D

Thanks!