to be: to exist, be present, become, or come to pass
This is Hebrew's all-purpose verb of being, and it covers far more ground than the English word "be." It can say that something exists or is present, that something turns into something else, or that an event takes place. Which of these a given verse means is usually decided by the words around it, especially the little words that follow it.
A key fact shapes how this verb is used. In ordinary Hebrew you can say "the LORD my shepherd" or "God a refuge for us" with no verb at all; the "is" is simply understood. So this verb tends to surface precisely when the plain wordless sentence will not do the job, above all when the writer needs to set a time (was, will be, used to be) or a mood (let it be). That is why it shows up so often in past-tense storytelling and in commands and promises, and far less in poetry.
One note of caution runs through the whole word. For much of the last century scholars claimed that this verb carries a built-in sense of dynamic movement or "becoming," supposedly unlike the static "to be" of Greek thought. The linguist James Barr showed in 1961 that this overreached: a verb's deep history does not secretly load every use with hidden meaning. The verb really does lean toward happening and becoming more than English "be" does, but each occurrence has to be read on its own, not forced to carry a grand idea.