Break it down by clauses first: [Tuus filius erit tutus,] [et Aeneae imperium perpetuum donabo.]
Tuus filius erit tutus: "Your son will be safe"
et Aeneae imperium perpetuum donabo: Look at the verb first. The verb is donabo, and because of the -o ending we know that the subject is "I." -abo is future tense. So first we have "and I will give."
Break it down again, paying attention to any words that agree with each other: et [Aeneae] [imperium perpetuum] [donabo.] We see that imperium and perpetuum go together, and there are two possibilities (nominative and accusative) since it is 2nd declension neuter. It has to be accusative, and not nominative, since the subject is already "I." Imperium perpetuum is the direct object of donabo. So translate that next: "And I will give perpetual power..."
Aeneae is dative, since it's the indirect object of donabo. So finally we have:
"Your son will be safe, and I will give perpetual power to Aeneas."
Things that I would recommend: (1.) Make a running spreadsheet or flashcard deck of all your vocabulary and quiz yourself on it some way. That way you'll be less stuck on having to look up what words mean. (2.) Memorize the forms of verbs and their meanings. You should know sum, esse and the forms of all conjugations. Just write them down over and over again, and check your work, until you know them. It will help a lot. (3.) Break down sentences and look for things you know go together. Look for the verb as it gives you valuable information on where to start.
Hope this helps!