"This is a nut."
There is only one article in Hebrew: ה (the). "That/this" (masc. זה/fem זהת) are referred to as demonstrative pronouns.
As for the question, in Hebrew it seems to be the case that feminine nouns often (always? don't know) end in ה, for instance boy is ילד and girl is ילדה. Vocab like man (גבר) and king (מלך) do not end in ה but the feminine יונה (dove) and יאשה (woman) do.
This is a bit confusing as the masculine demonstrative זה ends in ה whereas the feminine זהת ends in ת.
In Hebrew (like in many other languages) all nouns are gendered. They are always either masculine or feminine. אגוז is masculine but דרך, for instance, is feminine. That means that all the pronouns, adjectives and verbs need to align with their gender.
As for pen, עט (et) is masculine, like אורז, so it would be זה עט - this is a pen.
You can access them on your computer, or if you go through a web browser on your phone. They can't be accessed through the app. Once you are there, look for the light bulb, when you press on a particular skill. But know not every skill has a "tips and notes" section. Best of luck in your studies!