Tips and notes
THE ACCUSATIVE ENDING: -N
In Esperanto, a special ending is required to show that a noun is the direct object of a statement. Let's look at the English sentence "The girl reads a book." To show that a particular noun is a direct object (receives the action), always add an -n to the end of that noun or pronoun. Thus, the most usual translation of this sentence would be La knabino legas libron. Another way of thinking of this is to ask who or what is receiving the action, in this case a book libron.
Note that In English there is only one possible correct word order. However, due to Esperanto's accusative -n ending, all of the following are grammatically correct translations of "The girl reads a book":
La knabino legas libron. (most usual) La knabino libron legas. Legas knabino libron. Legas libron knabino. Libron knabino legas. (more emphasis on libron) Libron legas knabino. (also emphasis on libron)
Note that an adjective modifying a direct object would also receive the -n ending. Thus, Virino kisas belan viron. would mean "A woman kisses a handsome man." As explained above, we could also phrase this sentence as Belan viron kisas virino, which would still mean the same thing with more emphasis on the good-looking man.
Also, be aware that nouns used with "estas" never take the accusative ending: Li estas knabo.
There have been several comments in this section complaining about not being able to find tips.
So here is the best way to do it if you're on an android phone.
Open the Duolingo website in your browser and switch to desktop site. Now not only can you find the tips, you can also see how many experience points for the day have accumulated.
And, you can of course leave the tips page up and switch back and forth between the app and the browser when you need to look at something on the tips page again.
The -n is important. It tells you who is met. Without the -n, ili and viro both describe who is meeting but not who is met.
Ili renkontas la viron = They meet the man. Ilin renkontas la viro = The man meets them. La viron renkontas ili = They meet the man. La viro renkontas ilin = The man meets them.