No, they are not exactly the same in meaning. One is a simple statement of fact and the other has a connotation of scorn, as if a person has just said that cow is a horse and the answer was in disbelief that anyone would think such a silly thing. "A cow is no horse" is a declaration of disbelief and denial; there is an emotional element that is stronger than simply stating a fact.
You need the tips and notes. They're not on the app, you can find them broken down by level/skill http://duolingo.wikia.com/wiki/Duolingo_Wiki Or you can download every tip and notes for the whole course at https://www.docdroid.net/JnfmyEV/tipsnotesbackup.pdf
You've got a list of pronouns.
In the order you wrote them: it's/this (masculine/ and for plural, they (masculine), she, lastly is zot: it's/this feminine.זאת
, ,he הוא :
you left out I also recommend the memrise Duolingo Hebrew vocab course. This is the course I started before Duolingo: http://www.memrise.com/course/1031737/hebrew-duolingo/
It's all the vocab used in Duolingo broken up the same way Duolingo does with audio. But no grammar. I'm on #32, I've found it very helpful to know the vocab before using it sentences.
It needs a copula. Tips and notes for this skill Tips and notes Copula (אוגד) When we want to define a general feature of an object (i.e. lemons are sour), we use the copula (אוגד). The main purpose of the copula is to link the subject of a sentence with a predicate.
In simple terms, the copula is like the English verb "to be".
The copula in Hebrew uses the third person pronouns to describe objects (i.e. he/it הוא she/it היא they (m) הם they (f) הן).
Fish are tasty = דגים הם טעימים (literally - fish they (are) tasty).
This allows you to differentiate between: דגים טעימים - tasty fish and דגים הם טעימים - fish are tasty.
Definite articles with adjectives When adding definite articles to nouns with adjectives, both the noun and the adjective receive a definite article.
The big dog = הכלב הגדול (hakélev hagadól).
This rule is also applicable when we use more than one adjective for the same noun.
The big beautiful dog = הכלב הגדול והיפה (hakélev hagadól ve'hayafé). Note that we say "big and beautiful". הגדול היפה is not as natural as "big beautiful" as in English.
So now you can differentiate between:
הכלב גדול = The dog is big (ha'kelev gadol)
הכלב הגדול = The big dog (ha'kelev ha'gadol)
Possessives with adjectives When you have a noun, an (attributive) adjective and a possessive, the possessive comes after both the noun and the adjective:
הכלב החדש שלי My new dog
not הכלב שלי החדש