Learn French: C'est un arbre ou une fleur ?

In casual spoken French, you can turn a statement into a question just by raising your pitch at the end. So, c'est (it is) becomes c'est ... ? (is it ... ?). You don't have to change the word order like you do in English.

How do I pronounce C'est un?

There is a spoken link (called a liaison) between the normally silent t in est and the vowel u in un. You pronounce them together so it sounds like "seh-tun".

Why is it un arbre but une fleur?

French nouns have a gender. Arbre (tree) is a masculine word, so it uses the masculine word for "a" which is un. Fleur (flower) is feminine, so it uses une. It is always best to memorize the gender along with the vocabulary word!

Does ou mean "or" or "where"?

Here, ou (without an accent mark) means "or". The word for "where" is où (with a grave accent). They sound exactly the same when spoken, but the accent changes the meaning in writing.