What should I do when I read a new Latin text and there are words I don't know in the exam? I can't use a dictionary

You should be relaxed and read it first in a global way, paying attention to the structure of the text and those words you already know. Think outside of the box: pay special attention to the setting ( names of places and persons that appear in the text) , the genre in which the text is written ( elegy, philosophical text, historiographic text, etc) , the story that the text tells you, whether the text is written in verse or prose, etc. These general hints can provide you with the right tools to understand the text. Later, try to think about the internal structure of the text: what grammatical structures you can find, what words are repeated, how the text creates its own narrative. To sum up, it's good to tackle the text from many different perspectives, so when there are words or phrases you don't know in the exam you can have an educated guess about their meaning. This will enhance your reading skills and will allow you to do great in you exams!