How do i know when to put the latin word 'est' at the end of a sentence? For example: Scintilla fessa est, Scintilla est femina Why is 'est' in a different position in each of the above sentences.
As a general rule, Latin verbs go at the end of the sentence, including the verb sum. (Traditionally, Latin has been considered a "SOV" (subject, object, verb) language, though scholars have recently cast doubt upon the necessity of that claim.)
Having said that, verb placement can vary freely, mostly for pragmatic reasons---say if you want to emphasise the verb by placing it at the beginning of the sentence, or if you are answering a question, etc.
- Vēnistī herī? # Vēnī hodiē ("Did you come yesterday? # I came today")
Other times you may wish to make explicit an attributive (rather than an existential) use of sum. Compare:
Magnus sōl est ("The great sun exists / there is great sun")
Magnus est sōl ("The sun is great.")
In subordination constructions (such as Accusative + Infinitive) the main verb position can vary as well. E.g. all of these are semantically equivalent, but vary pragmatically:
Vergilius dīcit poētam arma virumque cecinisse ("Virgil says that the poet sung the arms and man")
Vergilius poētam arma virumque cecinisse dīcit
Dīcit Vergilius poētam arma virumque cecinisse, etc.