Counting and identifying iambs

I would love to write poetry forms with some sort of iambic forms, but I find it hard to count them and identify which is the stressed syllable and which is not.

So far I've read that you can break up the words into syllables and count one as stressed and one not, but I still don't know how to identify the stressed and unstressed ones. Is it arbitrary? Or is there a rule?

Does anyone here have a strategy for this?

Hi Zahra, it's not that complex.

I just use a dictionary whenever I don't know how to break down the syllables or when I don't know where the stress goes to.

http://dictionary.reference.com/

Type a word. Make sure is a two syllable one first just so you could see the difference. For instance, water. Then you will see that the stressed syllable is in bold

Then just write as if you would write free style but pay attention to the rhythm. And where the bold ones are. In my example, I'm just using capital letters to distinguish them.

Example:

A DUCK was QUACKing LOUD
That LAKES beGAN to QUAKE
And SOON a BEAR aWOKE
To ROAR then HIDE in SHRUBS.

That's a good tip... thanks :)