/ ˈ / shows the strong stress in a word or group of words. It is in front of the part (or syllable) that you say most strongly. For example, any /ˈɛni/ has a stress on the first syllable; depend /dɪˈpɛnd/ has a stress on the second syllable.
/ ˌ / shows a weaker (or secondary) stress. Many longer words have a syllable that is pronounced with a secondary stress as well as a syllable with strong (or main) stress. So in the word pronunciation /prəˌnʌnsiˈeɪʃn/, the main stress is on the syllable /ˈeɪ/, and the secondary stress is on the syllable /ˌnʌn/.