an operator for "contains"

k = c(1:9)
if( length( which(k==3) ) ){ print("contained") }else{ print("not contained") }

is therre a simple way to test if a vector/list contains a particular value?

Yes, several. Here's one:
k <- 1:9
if(any(k == 3)) {
cat("is an element\n") } else {
cat("not an element\n") }

I don't recommend that for floating point numbers, though.

more generally, is the a documentaion page that lists/describes all
such operators?

help("==") would get you the help page for the actual binary
operators. Since any() isn't an operator, that won't help.

lastly, if you didn't know the answer to my question, how would you have
gone about searching for an answer? 

There are a variety of ways to find answers in R, although if you
aren't certain what your keyword should be, it may take a few tries.

help(), help.search(), and apropos() may all be useful.

Sarah

Sarah Goslee
http://www.stringpage.com