I'll pick German, which - like ancient Greek - has three genders and four cases. Modern Greek dropped the dative but the other three are pretty much like the corresponding German ones.
So you have ο - η - το in the nominative case for masculine, feminine, and neuter nouns, respectively: like der - die - das.
And in the accusative case, you have τον - την - το: like den - die - das.
As in German, you should learn the gender of a noun along with the word itself, but in Greek, you can almost always guess the gender from the ending:
- masculine: -ος -ας -ης
- feminine: -α -η
- neuter: -μα -ι -ο
Nouns in -ος can be any of the three genders but are most often masculine. There are a couple of other exceptions as well (e.g. το γάλα, το κρέας which are neuter rather than feminine or masculine) but on the whole, it's pretty reliable.
One difference from German is that Greek has three genders in the plural as well, with articles οι - οι - τα in the nominative and τους - τις - τα in the accusative. (For gender distinction in plural articles, compare e.g. Spanish where el has plural los and la has plural las.)
The genitive case is του - της - του in the singular (des - der - des) and των in the plural for all three genders (der).
This "sentence" has the noun χρώμα, which is neuter, as you can guess from the ending -μα, so it takes the neuter article το.
Here you are. These links will not only show you how to get the Greek keyboard but also how to find the Greek letters on it.
It will also help you learn the alphabet and where to find other useful links.
And here is another to help you navigate Duolingo FAQ - General Questions, Bugs Reports https://www.duolingo.com/comment/23799672
Some simple rules to get you started:
Always read the comments before posting.
Read the Tips notes right below the list of lessons on your Home page
Read the drop down hints. Pass your cursor over a word and a list of words will appear.
The hints under the words are like a dictionary. As in a dictionary not every word shown is used in every sentence. The best thing to do is to always choose the first word shown.
Also, as you are new let me welcome you and think you will find this link helpful.