What is a particle? / “First” Particle は

A particle is a word that usually holds sentences together (am, is, are, and, etc…)

は is pronounce like わ. は would be used as am/is/are depending on tense in the sentence.
ぶどうはくがまのです。Grapes are fruits
So it would be in the format AはB。

For the sake of having examples, here’s a snippet of text from TextFugu using all of the tenses.