"ocean"

Translation: ωκεανός

[FrancineKa1]

why isn't it thalassa?

[panayiotis4]

Thalassa refers to the sea while okeanos refers to the ocean.

[Matis138245]

θάλασσα

[julesmGGF]

Would it be grammatically correct to put an omicron/add an article here as well?

[D_..]

Only if you do it in both languages. It's not a phrase; just a word translation. ;)

[renancam]

What's the difference between omega and omicron?

[G.Georgopoulos]

As far as their pronunciation is concerned, none. "Ο", however, can be part of the diphthongs "-οι-", which makes an "i" sound, and "-ου-", which makes a "u" sound.

The most fundamental orthography rule in the usage of "ω" is that, whenever a verb ends in an "-o" sound (that is, in the 1st person singular), it's always spelled with an "ω" ;)

[Elisa849218]

What's the difference between "ς" and "σ" ? Im lost

[jaye16]

First of all see here for lots of helpful links.

These links will not only show you how to get the Greek keyboard but also how to find the Greek letters on it, how to add accents etc.
https://www.duolingo.com/comment/22040507

Greek on Android and iOS!
https://www.duolingo.com/comment/20607862

This σ is used at the start or in the word and this one is only used at the end ς. They sound exactly the same.

See here for other hints to make learning easier.

TIPS TO HELP YOU LEARN + HOW TO REPORT A PROBLEM

https://forum.duolingo.com/comment/22424028