# path where your csv files are (here current working directory)
CSV_FOLDER <- "."

# list all csv files in given directory
# second parameter is a regex meaning ends with .csv
# third parameter make function return file names with path
csv_files <- list.files(CSV_FOLDER, "\\.csv$", full.names=TRUE)

# apply given function on each file and collect results in a list
res <- lapply(csv_files, function(csv_file) {
  # read current file
  tmp <- read_csv(csv_file)

  # build a data.frame from filename (without path) and mean of second column
  return(data.frame(
    name = basename(csv_file),
    meanofsecondcolumn = mean(tmp$second_column)
  ))
})

# rbind all single line data.frames in a single data.frame
res <- do.call("rbind", res)