And the old sailor said, "Firstly, I wish to tell you of the courage and the virtue of the Athenians*. I, to those whom are present who was there**, will clearly reveal the true cause(s) or all the Greeks will hand over their freedom*** which generated**** peace for the Greeks. Because (γάρ) we, living completely (ἐν πᾶσῃ) free for all of our lives, thought it IS not necessary that we fight barbarians over all the Greek's freedom.
"But our ancestors established a beautiful government. In other nations the citizens had tyrannies and oligarchies. We were not thinking it fitting that slaves and masters have the same equality of political rights according to law. We, however, didn't think it was correct for one to be slave or ruler to somebody else; instead, we pursued equality before the law. For (γάρ) we are were dear to one another and are we were all free, and we were yielding to nothing except for the notion of true virtue."
You weren't careful in some parts, namely in the part where you saw a "not" that isn't there and the part where you said "are" instead of "were". The more texts you translate/work on, the faster and easier it is going to become!
*"τέ" together with "καί" basically means "and", but it's more powerful than "καί".
So for example
Greeks and Barbarians = Ἕλληνες καί βάρβαροι.
Both Greeks AND Barbarians = Ἕλληνες τέ καί βάρβαροι.
**You see, the sailor was old, and is apparently talking to younger people who weren't alive when the things he is describing were going on!
***"ἥ" means "which" (feminine). "or" would be "ἤ"
****I couldn't find a better way to translate this phrase word to word. It means: I will reveal to you the reason for which the Greeks lived in peace. Or the reason which made the Greeks free. I will reveal to you why the Greeks are free.
Of course it's better not to translate word to word, but that will only come with experience.
Finally I'd like to say that obviously some parts in this text are hard for a beginner so don't be discouraged.