See help(normal), which covers qnorm and rnorm, as well as dnorm and qnorm.
The q and x arguments are vectors of quantiles. p is a vector of probabilites and n is a number of observations. In each case, these are positional, so it doesn't really matter how whether identified in the argument
dnorm(x = your_vector)
is equivalent to
dnorm(your_vector)
x <- 0
dnorm(x = 0) == 1/sqrt(2*pi)
#> [1] TRUE
dnorm(x) == 1/sqrt(2*pi)
#> [1] TRUE
As for the naming of the arguments, I speculate that these arise from conventions among statisticians.