1. The Case System: Nominative, Vocative & Accusative
Latin marks a noun's grammatical job with endings (case), not word order, so subject and object can appear in almost any position in the sentence.
Nominative = subject/predicate noun; Vocative = direct address (identical to nominative except 2nd-declension -us $arrow$ -e, e.g. Marce); Accusative = direct object, object of certain prepositions (ad, in + motion, per, ob, propter), and subject of an infinitive in indirect statement. 1st decl. acc. sg. -am/pl. -as; 2nd decl. -um/-os; 3rd decl. -em/-es.
Accusative subject of an infinitive (indirect statement) vs. accusative direct object of the main verb --- dico eum venire (``I say that he is coming'') has eum as subject of venire, not object of dico.
Translating the first noun encountered as the subject just because it is the first word in the sentence --- Latin word order is flexible, so the case ending, not position, identifies the subject.
No fixed word order $arrow$ trust the ending, not the position.