In R, a variable is either a function or a value. You must use
a <- 5 to assign
5 to the variable
a <- "test" b <- 5 a b # you can use assign # to change a variable value assign(a, b) # or simply use a <- 7
You can also use
=, but you should not, as this is overusing an operator that is supposed to do something else.
You can read the official note here.
Declare a variable
You can't declare a variable without giving it a value, but you can do something like this
r <- NULL
This is useful, as concatenating with NULL is working well
r <- NULL r <- c(r, 3) #  3
Print a variable
In R, every line is an expression. And if the result of the expression is a value, then it's printed, otherwise, you need to explicitly call print (or any printing function like cat).
r # implicit print(r) # explicit