Comments

Pine Script supports single-line comments. Any text from the symbol // until the end of the line is considered as comment. An example:

//@version=4
study("Test")
// This line is a comment
a = close // This is also a comment
plot(a)

The Pine Editor has a hotkey for commenting/uncommenting: Ctrl + /. Highlight a code fragment and press Ctrl + / to comment/uncomment whole blocks of code at a time.

Comments cannot be placed in the middle of a statement continued on multiple lines. Read more on this here: Line_wrapping.