Word stress                                                                                                                                                                              

When a word has many syllables, one of them is always pronounced more strongly. This is called word stress, and we say that the syllable is stressed. For example, in the word become, the stressed syllable is come.

Dictionaries tell you which syllable is stressed. The most popular system is to put a vertical line (´) before the stressed syllable in the phonetic transcription of the word. For example, the transcription for become /bɪˈkʌm/.

If a word has only one syllable (for example: pen, house), the syllable is always stressed. Dictionaries usually do not put the ˈ stress mark before the only syllable. So they don't write /ˈpen/ — they simply write /pen/.

Some dictionaries use other systems for showing word stress. For example, they may put an apostrophe after the stressed syllable, or they may underline the stressed syllable.

Interesting web pages on phonology                                                                                                                                   

What's in a sound?

Anglotic

English Phonetic Exercises

Ted Power: English Phonology

Trancription Exercises

Phonetics Focus: A Sound Choice