Learn French: Non, je plaisante !

In French, the simple present tense covers both "I joke" and "I am joking". You don't need to add a word for "am". Saying je plaisante translates perfectly to "I am joking" right now!

What is the base verb here, and how does it conjugate?

The infinitive (the base, dictionary form) is plaisanter (to joke). It is a regular -er verb. To say "I joke" or "I am joking", you drop the -er and add the present tense ending for je, which is an -e, leaving you with je plaisante.

Why does the "s" in plaisante sound like a "z"?

In French, when a single s is wedged right between two vowels (here, the i and the a), it makes a buzzy "z" sound. To get an "s" sound between vowels, French words use a double ss.

Do I pronounce the "e" at the end of plaisante?

No, the e at the end of plaisante is silent. However, because the e is there, it forces you to pronounce the consonant right before it, meaning the spoken word ends on a crisp "t" sound.