I'd or I would (not Id). You can look up these words in a dictionary and find example sentences. Try Oxford dictionary online. Some dictionaries also have Usage Notes which explain differences. Just one everyday example: A store can reduce or decrease its prices. Proper treatment of an injury can diminish or lessen the pain. You can also use 'reduce' and 'decrease' in the second sentence, but a store does not 'lessen' or 'diminish' prices, probably because 'prices' is a count noun, and pain is a mass/non-count noun.