write.table(...) function writes a matrix or data frame into a file. It's usage is:

write.table(x, file = "", append = FALSE, quote = TRUE, sep = " ",
eol = "\n", na = "NA", dec = ".", row.names = TRUE,
col.names = TRUE, qmethod = c("escape", "double"),
fileEncoding = "")
write.csv(x, file = "", append = FALSE, quote = TRUE, sep = " ",
eol = "\n", na = "NA", dec = ".", row.names = TRUE,
col.names = TRUE, qmethod = c("escape", "double"),
fileEncoding = "")
write.csv2(...)

x: The matrix or data frame to be written
file: Out file name, if empty, then print to the screen
append: Append model, otherwise new file will be created
sep: Seperator, default is " "
...


Let's see a matrix example (we will print to the screen, you may give a file name for writing to the file):

> x <- matrix(c(3,5,7,1,9,4),nrow=3,ncol=2,byrow=TRUE)
> write.table(x,"")

"V1" "V2"
"1" 3 5
"2" 7 1
"3" 9 4

Let's write into a file and use "," as field separator:

> write.table(x,"test.csv",sep=",")

The content of "test.csv" is:

"V1","V2"
"1",3,5
"2",7,1
"3",9,4