A question I’ve googled before without success. Hopefully this answer will show up for someone who needs it. I’ll also go over the better-known uses of ? just in case.

• To get help in R about a function like subset you type ?subset . That’s like man subset from the command line.
• If you only know roughly what you’re looking for use double question marks: so ??nonlinear will lead to the package nlme. That’s like apropos on the command line.
• To get a package overview, type ?xts::xts. There does not exist ?xts help. Packages that don’t have ?twitteR::twitteR you will need to use ??twitteR to find the help pages on ?twitteR::status-class, ?twitteR::dmGet, etc.
• Finally, the question of the title. To get R help on punctuation such as (, {, [, `, ::, ..., +, and yes, even on ? itself, use single quotes to ‘escape’ the meaningful symbol. Examples follow:
  • ?'`'
  • ?'('
  • ?'['
  • ?'...'
  • ?'+'
  • ?'%*%'
  • ?'%x%'
  • ?'%o%'
  • ?'%%'
  • ?'%/%'
  • ?'$'
  • ?'^'
  • ?'~'
  • ?'<-'
  • ?'='
  • ?'<<-'