I would like to make a polka dot pattern
In writing this I will make the assumption that you have read I would like to make a swiss dot pattern and so now know a few basics. If you haven't or if you get confused at any point during the tutorial can I suggest that you read that one first which is aimed at newbies.
To begin with open a window which is 2cm by 2 cm, with 300 resolution per inch, RGB and transparent.
Make sure you have your rulers out as positioning is a little more essential with a polka dot, but hey random is good to. Pull your rulers out to 1 cm. You should now have a screen that looks like this
As you can see you have divided the box into quarters. Looks nice and tidy doesn't it :)
Take your brush, any colour any size and put a dot in the first box. Now resize the dot til it is the size you want but stay in the first box. Do you like it? Now with your eye center the dot.
It doesn't have to be exact, but if you do want it to be exact you can pull out your rulers again this time to 0.5 each way.
Once you have your dot duplicate it by clicking on your layer in the layer box and then pulling it down to the new layer icon which is the tiny box that you use to make new layers. Drop it there. It is a tricky little thing but once you get used to doing it you will wonder how you got by without it.
Now you have two dots exactly the same one on top of the other. Click on the dot in the first box and drag it to the forth box. You now have two dots that are identical in a diagonal formation and in the center of their own little boxes. Nice work :)
If you have done the swiss dot pattern you will know you are nearly there now. Click on the edit tab at the top of the page and go down to define pattern. In the box name your pattern...polka dot seems about right...and then click ok.
Open a new widow 30cm by 30 cm same specifications as before.
In the new window go to layer, the button on the top tool bar, then new fill layer, and then pattern. Polka dot should be the top pattern so just click ok.
Ta da, you are now the proud owner of a page of perfectly spaced polka dots!
I have scaled them up so you can see them better.
There is so much you can now do with your new polka dots. Perhaps you would like them a different color.
Make a new layer and fill with the color of your choice. Now click on control g (actually one of my favourite control buttons) and your new dots will have changed to your new color.
Or perhaps you have a piece of background paper that you really like and you would like to put over your dots. Well put that in a new layer directly above the dots and click control g again.
Things I can do with my new found knowledge
You can use the knowlege you have learned above to make lots of different patterns. Consider taking a nice flower that you already have and putting that in each of the boxes. Perhaps tilt each flower a slightly different direction for interest.
I have put them on a plain pink background so you can see them, but you could choose another patterned one. Pretty isn't it?
Perhaps next time try one Explore what you can do with it and above all don't be afraid to play around with photoshop, after all, you paid for it :)