Not sure entirely what you are asking, but most packages provide a vignette that includes the function prototypes and example usages.
If you have a package loaded in your R environment, you can view the source by entering the function name to the console.
As an arbitrary example:
>> library(deSolve)
>> ode
function (y, times, func, parms, method = c("lsoda", "lsode",
"lsodes", "lsodar", "vode", "daspk", "euler", "rk4", "ode23",
"ode45", "radau", "bdf", "bdf_d", "adams", "impAdams", "impAdams_d",
"iteration"), ...)
{
if (is.null(method))
method <- "lsoda"
if (is.list(method)) {
if (!"rkMethod" %in% class(method))
stop("'method' should be given as string or as a list of class 'rkMethod'")
out <- rk(y, times, func, parms, method = method, ...)
}
else if (is.function(method))
out <- method(y, times, func, parms, ...)
else if (is.complex(y))
out <- switch(match.arg(method), vode = zvode(y, times,
func, parms, ...), bdf = zvode(y, times, func, parms,
mf = 22, ...), bdf_d = zvode(y, times, func, parms,
mf = 23, ...), adams = zvode(y, times, func, parms,
mf = 10, ...), impAdams = zvode(y, times, func, parms,
mf = 12, ...), impAdams_d = zvode(y, times, func,
parms, mf = 13, ...))
else out <- switch(match.arg(method), lsoda = lsoda(y, times,
func, parms, ...), vode = vode(y, times, func, parms,
...), lsode = lsode(y, times, func, parms, ...), lsodes = lsodes(y,
times, func, parms, ...), lsodar = lsodar(y, times, func,
parms, ...), daspk = daspk(y, times, func, parms, ...),
euler = rk(y, times, func, parms, method = "euler", ...),
rk4 = rk(y, times, func, parms, method = "rk4", ...),
ode23 = rk(y, times, func, parms, method = "ode23", ...),
ode45 = rk(y, times, func, parms, method = "ode45", ...),
radau = radau(y, times, func, parms, ...), bdf = lsode(y,
times, func, parms, mf = 22, ...), bdf_d = lsode(y,
times, func, parms, mf = 23, ...), adams = lsode(y,
times, func, parms, mf = 10, ...), impAdams = lsode(y,
times, func, parms, mf = 12, ...), impAdams_d = lsode(y,
times, func, parms, mf = 13, ...), iteration = iteration(y,
times, func, parms, ...))
return(out)
}
<environment: namespace:deSolve>