iambic pentameter
This line is in iambic pentameter because it has ten syllables that alternate unstressed then stressed.
 u        /       u         /         u         /         u      /      u       /
To | swell | the | gourd,| and | plump | the | ha | zel | shells
  1      2       3        4         5         6        7      8     9      10
When trying to identify meter and rhythm, start with two syllable words-this will help identify where some stresses sit in the line.